query: Buy/Selling prices at the stock exchange represent someone Selling/Buying at that price?

positive: You don't see Buying and Selling. You see Bid and Ask. Best Bid--Highest Price someone is willing to pay to buy a stock. Best Ask - Lowest price someone is willing to accept to sell a stock. As for your second question, if you can look up Accumulation/Distribution Algorithm and Iceberg Order, you will get basic idea.

negative: "Well, futures don't have a ""strike"" like an option - the price represents how much you're obligated to buy/sell the index for at a specified date in the future.  You are correct that there's no cost to enter a contract (though there may be broker fees and margin payments).  Any difference between the contract price and the price of the index at settlement is what is exchanged at settlement.   It's analogous to the bid/ask on a stock - the bid price represents the price at which someone is willing to ""buy"" a futures contract (meaning enter into a long position) and the ask is how much someone is willing to ""sell"" a contract. So if you want to take a long position on S&P500 mini futures you'd have to enter in at the ""ask"" price.  If the index is above your contract price on the future expiry date you'll make a profit; if it is below the contract price you'll take a loss."

negative: "There are several reasons. First, if you sell your stock ""at any price"", you may be selling it for less than you originally bought it for.  Thus you will take a loss right at the beginning of your scheme.  If you ""rinse and repeat"", the problem only gets worse.  Every time you sell your stock, you will have to sell it at an even lower price in order to lower the price even more.  Then you buy it back and. . . just resell it an even lower price?  It should be clear that you are not making any money this way. Second, even if you don't sell it at an absolute loss, you must sell it at a relative loss in order to lower the price.  In other words, if someone will currently buy your shares for $X, and you want to lower the price, you must sell them for less than $X.  But you could have made more money by selling them for $X, since someone was already willing to buy them at that price.  In order to bring the price down significantly, you have to sell the stock for less than people currently believe it is worth, which means you're incurring a loss relative to just selling it at the market rate.  Of course, you can still make money if it goes back up again, but selling it at an extra loss this way just makes it harder to break even. Third, if you sell the stock at $X, whoever you sold it to is not going to sell it right back to you at $X, because then they would not make any money.  You could in theory buy it from someone else, but the same principle holds: if the stock price has just gone down, people who have it may be waiting for it to go back up.  This is doubly true if anyone suspects you have been trying to manipulate the stock price, because they will then suspect that the price drop is artificial and it will soon go back up. Fourth, even if someone did sell it right back to you at the price you sold it for, then what?  You now hold the stock at a lower price, but you don't gain unless it goes back up.  If it wasn't going up before until you took action, there is no reason to suppose it will go back up now.  In fact, if you had enough shares to significantly influence the price, other people may have been fooled into thinking the value is actually lower now. The basic problem is that, in order for you to buy it at a low price, someone else has to sell it at that low price.  It is easy to sell someone a stock for less than it's worth, but it will be hard to get people to sell it back to you for less than it's worth.  If you engage in deceptive practices to get people to do this, you may be guilty of securities fraud."

negative: "I think you've got basics, but you may have the order / emphasis a bit wrong. I've changed the order of the things you've learned in to what I think is the most important to understand: Owning a stock is like owning a tiny chunk of the business Owning stock is owning a tiny chunk of the business, it's not just ""like"" it. The ""tiny chunks"" are called shares, because that is literally what they are, a share of the business. Sometimes shares are also called stocks. The words stock and share are mostly interchangeable, but a single stock normally means your holding of many shares in a business, so if you have 100 shares in 1 company, that's a stock in that company, if you then buy 100 shares in another company, you now own 2 stocks. An investor seeks to buy stocks at a low price, and sell when the price is high. Not necessarily. An investor will buy shares in a company that they believe will make them a profit. In general, a company will make a profit and distribute some or all of it to shareholders in the form of dividends. They will also keep back a portion of the profit to invest in growing the company. If the company does grow, it will grow in value and your shares will get more valuable. Price (of a stock) is affected by supply/demand, volume, and possibly company profits The price of a share that you see on a stock ticker is the price that people on the market have exchanged the share for recently, not the price you or I can buy a share for, although usually if people on the market are buying and selling at that price, someone will buy or sell from you at a similar sort of price. In theory, the price will be the companies total value, if you were to own the whole thing (it's market capitalisation) divided by the total number of shares that exist in that company. The problem is that it's very difficult to work out the total value of a company. You can start by counting the different things that it owns (including things like intellectual property and the knowledge and experience of people who work there), subtract all the money it owes in loans etc., and then make an allowance for how much profit you expect the company to make in the future. The problem is that these numbers are all going to be estimates, and different peoples estimates will disagree. Some people don't bother to estimate at all. The market makers will just follow supply and demand. They will hold a few shares in each of many companies that they are interested in. They will advertise a lower price that they are willing to buy at and a higher price that they will sell at all the time. When they hold a lot of a share, they will price it lower so that people buy it from them. When they start to run out, they will price it higher. You will never need to spend more than the market makers price to buy a share, or get less than the market makers price when you come to sell it (unless you want to buy or sell more shares than they are willing to). This is why stock price depends on supply and demand. The other category of people who don't care about the companies they are trading are the high speed traders. They just look at information like the past price, the volume (total amount of shares being exchanged on the market) and many other statistics both from the market and elsewhere and look for patterns. You cannot compete with these people - they do things like physically locate their servers nearer to the stock exchanges buildings to get a few milliseconds time advantage over their competitors to buy shares quicker than them."

negative: You are misunderstanding what makes the price of a stock go up and down. Every time you sell a share of a stock, there is someone else that buys the stock.  So it is not accurate to say that stock prices go down when large amounts of the stock are sold, and up when large amounts of the stock are bought.  Every day, the amount of shares of a stock that are bought and sold are equal to each other, because in order to sell a share of stock, someone has to buy it. Let me try to explain what actually happens to the price of a stock when you want to sell it. Let's say that a particular stock is listed on the ticker at $100 a share currently.  All this means is that the last transaction that took place was for $100; someone sold their share to a buyer for $100. Now let's say that you have a share of the stock you'd like to sell.  You are hoping to get $100 for your share.  There are 2 other people that also have a share that they want to sell.  However, there is only 1 person that wants to buy a share of stock, and he only wants to pay $99 for a share.  If none of you wants to sell lower than $100, then no shares get sold.  But if one of you agrees to sell at $99, then the sale takes place.  The ticker value of the stock is now $99 instead of $100. Now let's say that there are 3 new people that have decided they want to buy a share of the stock.  They'd like to buy at $99, but you and the other person left with a share want to sell at $100.  Either one of the sellers will come down to $99 or one of the buyers will go up to $100.  This process will continue until everyone that wants to sell a share has sold, and everyone who wants to buy a share has bought.  In general, though, when there are more people that want to sell than buy, the price goes down, and when there are more people that want to buy than sell, the price goes up. To answer your question, if your selling of the stock had caused the price to go down, it means that you would have gotten less money for your stock than if it had not gone down.  Likewise, if your buying the stock had caused it to go up, it just means that it would have cost you more to buy the stock.  It is just as likely that you would lose money doing this, rather than gain money.

negative: "This is a complicated subject, because professional traders don't rely on brokers for stock quotes.  They have access to market data using Level II terminals, which show them all of the prices (buy and sell) for a given stock.   Every publicly traded stock (at least in the U.S.) relies on firms called ""market makers"".  Market makers are the ones who ultimately actually buy and sell the shares of companies, making their money on the difference between what they bought the stock at and what they can sell it for.  Sometimes those margins can be in hundreds of a cent per share, but if you trade enough shares...well, it adds up. The most widely traded stocks (Apple, Microsoft, BP, etc) may have hundreds of market makers who are willing to handle share trades.  Each market maker sets their own price on what they'll pay (the ""bid"") to buy someone's stock who wants to sell and what they'll sell (the ""ask"") that share for to someone who wants to buy it.   When a market maker wants to be competitive, he may price his bid/ask pretty aggressively, because automated trading systems are designed to seek out the best bid/ask prices for their trade executions.  As such, you might get a huge chunk of market makers in a popular stock to all set their prices almost identically to one another.  Other market makers who aren't as enthusiastic will set less competitive prices, so they don't get much (maybe no) business.  In any case, what you see when you pull up a stock quote is called the ""best bid/ask"" price.  In other words, you're seeing the highest price a market maker will pay to buy that stock, and the lowest price that a market maker will sell that stock.  You may get a best bid from one market maker and a best ask from a different one.  In any case, consumers must be given best bid/ask prices. Market makers actually control the prices of shares.  They can see what's out there in terms of what people want to buy or sell, and they modify their prices accordingly.  If they see a bunch of sell orders coming into the system, they'll start dropping prices, and if people are in a buying mood then they'll raise prices. Market makers can actually ignore requests for trades (whether buy or sell) if they choose to, and sometimes they do, which is why a limit order (a request to buy/sell a stock at a specific price, regardless of its current actual price) that someone places may go unfilled and die at the end of the trading session.  No market maker is willing to fill the order. Nowadays, these systems are largely automated, so they operate according to complex rules defined by their owners.  Very few trades actually involve human intervention, because people can't digest the information at a fast enough pace to keep up with automated platforms. So that's the basics of how share prices work.  I hope this answered your question without being too confusing! Good luck!"

negative: "I may be underestimating your knowledge of how exchanges work; if so, I apologize.  If not, then I believe the answer is relatively straightforward. Lets say price of a stock at time t1 is 15$ .  There are many types of price that an exchange reports to the public (as discussed below); let's say that you're referring to the most recent trade price.  That is, the last time a trade executed between a willing buyer and a willing seller was at $15.00. Lets say a significant buy order of 1M shares came in to the market. Here I believe might be a misunderstanding on your part.  I think you're assuming that the buy order must necessarily be requesting a price of $15.00 because that was the last published price at time t1.  In fact, orders can request any price they want.  It's totally okay for someone to request to buy at $10.00.  Presumably nobody will want to sell to him, but it's still a perfectly valid buy order. But let's continue under the assumptions that at t1: This makes the bid $14.99 and the ask $15.00.  (NYSE also publishes these prices.) There aren't enough people selling that stock. It's quite rare (in major US equities) for anyone to place a buy order that exceeds the total available shares listed for sale at all prices.  What I think you mean is that 1M is larger than the amount of currently-listed sell requests at the ask of $15.00. So say of the 1M only 100,000 had a matching sell order and others are waiting. So this means that there were exactly 100,000 shares waiting to be sold at the ask of $15.00, and that all other sellers currently in the market told NYSE they were only willing to sell for a price of $15.01 or higher.  If there had been more shares available at $15.00, then NYSE would have matched them. This would be a trigger to the automated system to start increasing the price. Here is another point of misunderstanding, I think.  NYSE's automated system does not invent a new, higher price to publish at this point.  Instead it simply reports the last trade price (still $15.00), and now that all of the willing sellers at $15.00 have been matched, NYSE also publishes the new ask price of $15.01.  It's not that NYSE has decided $15.01 is the new price for the stock; it's that $15.01 is now the lowest price at which anyone (known to NYSE) is willing to sell.  If nobody happened to be interested in selling at $15.01 at t1, but there were people interested in selling at $15.02, then the new published ask would be $15.02 instead of $15.01 -- not because NYSE decided it, but just because those happened to be the facts at the time. Similarly, the new bid is most likely now $15.00, assuming the person who placed the order for 1M shares did not cancel the remaining unmatched 900,000 shares of his/her order.  That is, $15.00 is now the highest price at which anyone (known to NYSE) is willing to buy. How much time does the automated system wait to increment the price, the frequency of the price change and by what percentage to increment etc. So I think the answer to all these questions is that the automated system does none of these things.  It merely publishes information about (a) the last trade price, (b) the price that is currently the lowest price at which anyone has expressed a willingness to sell, and (c) the price that is currently the highest price at which anyone has expressed a willingness to buy. ::edit:: Oh, I forgot to answer your primary question. Can we estimate the impact of a large buy order on the share price? Not only can we estimate the impact, but we can know it explicitly.  Because the exchange publishes information on all the orders it knows about, anyone tracking that information can deduce that (in this example) there were exactly 100,000 shares waiting to be purchased at $15.00.  So if a ""large buy order"" of 1M shares comes in at $15.00, then we know that all of the people waiting to sell at $15.00 will be matched, and the new lowest ask price will be $15.01 (or whatever was the next lowest sell price that the exchange had previously published)."

negative: "If there is a very sudden and large collapse in the exchange rate then because algorithmic trades will operate very fast it is possible to determine “x” immediately after the change in exchange rate. All you need to know is the order book. You also need to assume that the algorithmic bot operates faster than all other market participants so that the order book doesn’t change except for those trades executed by the bot. The temporarily cheaper price in the weakened currency market will rise and the temporarily dearer price in the strengthened currency market will fall until the prices are related by the new exchange rate. This price is determined by the condition that the total volume of buys in the cheaper market is equal to the total volume of sells in the dearer market.   Suppose initially gold is worth $1200 on NYSE or £720 on LSE. Then suppose the exchange rate falls from r=0.6 £/$ to s=0.4 £/$.  To illustrate the answer lets assume that before the currency collapse the order book for gold on the LSE and NYSE looks like: GOLD-NYSE   Sell (100 @ $1310) Sell (100 @ $1300) <——— Sell (100 @ $1280) Sell (200 @ $1260) Sell (300 @ $1220) Sell (100 @ $1200) ————————— buy (100 @ $1190) buy (100 @ $1180)   GOLD-LSE Sell (100 @ £750) Sell (100 @ £740) ————————— buy (200 @ £720) buy (200 @ £700) buy (100 @ £600) buy (100 @ £550) buy (100 @ £530) buy (100 @ £520) <——— buy (100 @ £500)   From this hypothetical example, the automatic traders will buy up the NYSE gold and sell the LSE gold in equal volume until the price ratio ""s"" is attained. By summing up the sell volumes on the NYSE and the buy volumes on the LSE, we see that the conditions are met when the price is $1300 and £520. Note 800 units were bought and sold.   So “x” depends on the available orders in the order book. Immediately after this, however, the price of the asset will be subject to the new changes of preference by the market participants. However, the price calculated above must be the initial price, since otherwise an arbitrage opportunity would exist."

negative: Rebates are offered on exchange to promote liquidity offers so that aggressive buy/sell can be done, otherwise a sizable sell/buy would crash the price of a stock with no liquidity, it is perfectly normal for a firm to attempt look for the rebate if the customer is willing to wait longer for the execution to happen. The Author clearly has no freaking idea what the hell he is talking about.

negative: "Just read the book Flash Boys by Michael Lewis.  It describes this process in detail, albeit a bit more dramatically than it has to.  Basically what ""HFTs"" (high frequency traders) do is they set up their line to the exchange so its microseconds faster than everyone else.  Then they test out the market with tiny orders, seeing how fast it's getting filled - if these are getting filled immediately, it probably means there's a big order coming in from an investor.  So the algorithm - and it's all algo-based obviously because no human can remotely hope to catch this - will detect that as soon as there's a spike in volume, it will buy all of the volume at the current price, and sell it back for higher, forcing the big investor to take on higher prices.    Another case is that some HFTs can basically buy the entire trade book from an exchange like Nasdaq.  So every time someone places a market order for 200 shares of a 6.5 stock, the HFT will see it, buy up all the current stock from say 6.5-6.6 and sell it back at 6.7.  Not rocket science if you already get info about the trade coming in, in fact this is basically market making but performed by an ""evil HFT"" instead of a ""trustworthy bank.""    But honestly there are a lot more ways to make money from HFT than front-running, which isn't even possible anymore because exchanges no longer sell their books to HFTs."

negative: "There are two distinct questions that may be of interest to you. Both questions are relevant for funds that need to buy or sell large orders that you are talking about. The answer depends on your order type and the current market state such as the level 2 order book. Suppose there are no iceberg or hidden orders and the order book (image courtesy of this question) currently is:  An unlimited (""at market"") buy order for 12,000 shares gets filled immediately: it gets 1,100 shares at 180.03 (1,100@180.03), 9,700 at 180.04 and 1,200 at 180.05. After this order, the lowest ask price becomes 180.05 and the highest bid is obviously still 180.02 (because the previous order was a 'market order'). A limited buy order for 12,000 shares with a price limit of 180.04 gets the first two fills just like the market order: 1,100 shares at 180.03 and 9,700 at 180.04. However, the remainder of the order will establish a new bid price level for 1,200 shares at 180.04. It is possible to enter an unlimited buy order that exhausts the book. However, such a trade would often be considered a mis-trade and either (i) be cancelled by the broker, (ii) be cancelled or undone by the exchange, or (iii) hit the maximum price move a stock is allowed per day (""limit up""). Funds and banks often have to buy or sell large quantities, just like you have described. However they usually do not punch through order book levels as I described before. Instead they would spread out the order over time and buy a smaller quantity several times throughout the day. Simple algorithms attempt to get a price close to the time-weighted average price (TWAP) or volume-weighted average price (VWAP) and would buy a smaller amount every N minutes. Despite splitting the order into smaller pieces the price usually moves against the trader for many reasons. There are many models to estimate the market impact of an order before executing it and many brokers have their own model, for example Deutsche Bank. There is considerable research on ""market impact"" if you are interested. I understand the general principal that when significant buy orders   comes in relative to the sell orders price goes up and when a   significant sell order comes in relative to buy orders it goes down. I consider this statement wrong or at least misleading. First, stocks can jump in price without or with very little volume. Consider a company that releases a negative earnings surprise over night. On the next day the stock may open 20% lower without any orders having matched for any price in between. The price moved because the perception of the stocks value changed, not because of buy or sell pressure. Second, buy and sell pressure have an effect on the price because of the underlying reason, and not necessarily/only because of the mechanics of the market. Assume you were prepared to sell HyperNanoTech stock, but suddenly there's a lot of buzz and your colleagues are talking about buying it. Would you still sell it for the same price? I wouldn't. I would try to find out how much they are prepared to buy it for. In other words, buy pressure can be the consequence of successful marketing of the stock and the marketing buzz is what changes the price."

negative: In order to see whether you can buy or sell some given quantity of a stock at the current bid price, you need a counterparty (a buyer) who is willing to buy the number of stocks you are wishing to offload. To see whether such a counterparty exists, you can look at the stock's order book, or level two feed. The order book shows all the people who have placed buy or sell orders, the price they are willing to pay, and the quantity they demand at that price. Here is the order book from earlier this morning for the British pharmaceutical company, GlaxoSmithKline PLC.  Let's start by looking at the left-hand blue part of the book, beneath the yellow strip. This is called the Buy side. The book is sorted with the highest price at the top, because this is the best price that a seller can presently obtain. If several buyers bid at the same price, then the oldest entry on the book takes precedence. You can see we have five buyers each willing to pay 1543.0 p (that's 1543 British pence, or £15.43) per share. Therefore the current bid price for this instrument is 1543.0. The first buyer wants 175 shares, the next, 300, and so on. The total volume that is demanded at 1543.0p is 2435 shares. This information is summarized on the yellow strip: 5 buyers, total volume of 2435, at 1543.0. These are all buyers who want to buy right now and the exchange will make the trade happen immediately if you put in a sell order for 1543.0 p or less. If you want to sell 2435 shares or fewer, you are good to go. The important thing to note is that once you sell these bidders a total of 2435 shares, then their orders are fulfilled and they will be removed from the order book. At this point, the next bidder is promoted up the book; but his price is 1542.5, 0.5 p lower than before. Absent any further changes to the order book, the bid price will decrease to 1542.5 p. This makes sense because you are selling a lot of shares so you'd expect the market price to be depressed. This information will be disseminated to the level one feed and the level one graph of the stock price will be updated. Thus if you have more than 2435 shares to sell, you cannot expect to execute your order at the bid price in one go. Of course, the more shares you are trying to get rid of, the further down the buy side you will have to go. In reality for a highly liquid stock as this, the order book receives many amendments per second and it is unlikely that your trade would make much difference. On the right hand side of the display you can see the recent trades: these are the times the trades were done (or notified to the exchange), the price of the trade, the volume and the trade type (AT means automatic trade).  GlaxoSmithKline is a highly liquid stock with many willing buyers and sellers. But some stocks are less liquid. In order to enable traders to find a counterparty at short notice, exchanges often require less liquid stocks to have market makers. A market maker places buy and sell orders simultaneously, with a spread between the two prices so that they can profit from each transaction. For instance Diurnal Group PLC has had no trades today and no quotes. It has a more complicated order book, enabling both ordinary buyers and sellers to list if they wish, but market makers are separated out at the top. Here you can see that three market makers are providing liquidity on this stock, Peel Hunt (PEEL), Numis (NUMS) and Winterflood (WINS). They have a very unpalatable spread of over 5% between their bid and offer prices. Further in each case the sum total that they are willing to trade is 3000 shares. If you have more than three thousand Dirunal Group shares to sell, you would have to wait for the market makers to come back with a new quote after you'd sold the first 3000.

negative: NSCC illiquid charges are charges that apply to the trading of low-priced over-the counter (OTC) securities with low volumes. Open net buy quantity represents the total unsettled share amount per stock at any given time during a 3-day settlement cycle. Open net buy quantity must be less than 5,000,000 shares per stock for your entire firm Basically, you can't hold a long position of more than 5 million shares in an illiquid OTC stock without facing a fee. You'll still be assessed this fee if you accumulate a long position of this size by breaking your purchase up into multiple transactions. Open net sell quantity represents the total unsettled share amount per stock at any given time during a 3-day settlement cycle. Open net sell quantity must be less than 10% percent of the 20-day average volume If you attempt to sell a number of shares greater than 10% of the stock's average volume over the last 20 days, you'll also be assessed a fee. The first link I included above is just an example, but it makes the important point: you may still be assessed a fee for trading OTC stocks even if your account doesn't meet the criteria because these restrictions are applied at the level of the clearing firm, not the individual client.  This means that if other investors with your broker, or even at another broker that happens to use the same clearing firm, purchase more than 5 million shares in an individual OTC stock at the same time, all of your accounts may face fees, even though individually, you don't exceed the limits. Technically, these fees are assessed to the clearing firm, not the individual investor, but usually the clearing firm will pass the fees along to the broker (and possibly add other charges as well), and the broker will charge a fee to the individual account(s) that triggered the restriction. Also, remember that when buying OTC/pink sheet stocks, your ability to buy or sell is also contingent on finding someone else to buy from/sell to. If you purchase 10,000 shares one day and attempt to sell them sometime in the future, but there aren't enough buyers to buy all 10,000 from you, you might not be able to complete your order at the desired price, or even at all.

negative: When your options vest, you will have the option to buy your company's stock at a particular price (the strike price). A big part of the value of the option is the difference between the price that your company's stock is trading at, and the strike price of the option. If the price of the company stock in the market is lower than the strike price of the option, they are almost worthless.  I say 'almost' because there is still the possibility that the stock price could go up before the options expire. If your company is big enough that their stock is not only listed on an exchange, but there is an active options market in your company's stock, you could get a feel for what they are worth by seeing what the market is willing to buy or sell similar exchange listed options. Once the options have vested, you now have the right to purchase your company's stock at the specified strike price until the options expire.  When you use that right, you are exercising the option.  You don't have to do that until you think it is worthwhile buying company stock at that price. If the company pays a dividend, it would probably be worth exercising the options sooner, (options don't receive a dividend).  Ultimately you are buying your company's stock (albeit at a discount).  You need to see if your company's stock is still a good investment. If you think your company has growth prospects, you might want to hold onto the stock.  If you think you'd be better off putting your money elsewhere in the market, sell the stock you acquired at a discount and use the money to invest in something else. If there are any additional benefits to holding on to the stock for a period of time (e.g. selling part to fit within your capital gain allowance for that year) you should factor that into your investment decision, but it shouldn't force you to invest in, or remain invested in something you would otherwise view as too risky to invest in. A reminder of that fact is that some employees of Enron invested their entire retirement plans into Enron stock, so when Enron went bankrupt, these employees not only lost their job but their savings for retirement as well...

negative: The Limit Order are matched based on amount and time. The orders are listed Highest to Lowest on the Buy Side. The orders are listed Lowest to Highest on the Sell Side. If there are 2 Sell orders for same amount the order which is first in time [fractions of milliseconds] is first.  The about is the example as to how the orders would look like on any exchange.  Now the highest price the buyer is ready to pay is 20.21 and the lowest price a seller is ready to sell for is 20.25. Hence there is no trade. Now if a new Buy order comes in at 20.25, it matches with the sell and the deal is made. If a new Buy order comes in at 20.30, it still matches at 20.25. Similarly if a Sell order come in at 20.21, it matches and a deal is made. If a Sell order come in at 20.11, it still matches 20.21.   Incase of market order, with the above example if there is a Buy order, it would match with the lowest sell order at 20.25, if there is not enough quantity , it would match the remaining quantity to the next highest at 20.31 and continue down. Similarly if there is a Sell market order, the it would match to the maximum a seller is ready to buy, ie 20.21, if there is not sufficient buy quantity at 20.21, it will match with next for 20.19   If say there are new buy order at 20.22 and sell orders at 20.24, these will sit first the the above queue to be matched. In your above example the Lowest Sell order was at 20.10 at time t1 and hence any buy order after time t1 for amount 20.10 or greater would match to this and the price would be 20.10. However if the Buy order was first ie at t1 there was a buy order for 20.21 and then at time later than t1, there is a sell order for say 20.10 [amount less than or equal to 20.21] it would match for 20.21. Essentially the market looks at who was the first to sell at lower price or who was the first to buy at higher price and then decide the trade.  Edit [To Clarify xyz]: Say if there is an Sell order at $10 Qty 100. There is a buyer who is willing to pay Max $20 and is looking for Qty 500. Your key assumption that the Buyer does not know the current SELL price of $10 is incorrect. Now there are multiple things, the Buyer knows the lowest Sell order is at $10, he can put a matching Buy order at $10 Qty 100, and say $11 Qty 100 etc. This is painful. Second, lets say he puts a Buy order at $10 Qty 100, by the time the order hits the system someone else has put the trade at $10 and his order is fulfilled. So this buyer has to keep looking at booking and keep making adjustments, if its a large order, it would be extremely difficult and frustrating for this Buyer. Hence the logic of giving preference. The later Buy order says ... The Max I can pay is $20, match eveything at the current price and get the required shares.

negative: "It's simply supply and demand.   First, demand: If you're an importer trying to buy from overseas, you'll need foreign currency, maybe Euros.  Or if you want to make a trip to Europe you'll need to buy Euros.  Or if you're a speculator and think the USD will fall  in value, you'll probably buy Euros. Unless there's someone willing to sell you Euros for dollars, you can't get any.  There are millions of people trying to exchange currency all over the world.  If more want to buy USD, than that demand will positively influence the price of the USD (as measured in Euros).  If more people want to buy Euros, well, vice versa. There are so many of these transactions globally, and the number of people and the nature of these transactions change so continuously, that the prices (exchange rates) for these currencies fluctuate continuously and smoothly. Demand is also impacted by what people want to buy and how much they want to buy it.  If people generally want to invest their savings in stocks instead of dollars, i.e., if lots of people are attempting to buy stocks (by exchanging their dollars for stock), then the demand for the dollar is lower and the demand for stocks is higher.  When the stock market crashes, you'll often see a spike in the exchange rate for the dollar, because people are trying to exchange stocks for dollars (this represents a lot of demand for dollars). Then there's ""Supply:"" It may seem like there are a fixed number of bills out there, or that supply only changes when Bernanke prints money, but there's actually a lot more to it than that.  If you're coming from Europe and want to buy some USD from the bank, well, how much USD does the bank ""have"" and what does it mean for them to have money?  The bank gets money from depositors, or from lenders.  If one person puts money in a deposit account, and then the bank borrows that money from the account and lends it to a home buyer in the form of a mortgage, the same dollar is being used by two people.  The home buyer might use that money to hire a carpenter, and the carpenter might put the dollar back into a bank account, and the same dollar might get lent out again.  In economics this is called the ""multiplier effect."" The full supply of money being used ends up becoming harder to calculate with this kind of debt and re-lending.   Since money is something used and needed for conducting of transactions, the number of transactions being conducted (sometimes on credit) affects the ""supply"" of money. Demand and supply blur a bit when you consider people who hoard cash.  If I fear the stock market, I might keep all my money in dollars.  This takes cash away from companies who could invest it, takes the cash out of the pool of money being used for transactions, and leaves it waiting under my mattress.  You could think of my hoarding as a type of demand for currency, or you could think of it as a reduction in the supply of currency available to conduct transactions. The full picture can be a bit more complicated, if you look at every way currencies are used globally, with swaps and various exchange contracts and futures, but this gives the basic story of where prices come from, that they are not set by some price fixer but are driven by market forces.   The bank just facilitates transactions.  If the last price (exchange rate) is 1.2 Dollars per Euro, and the bank gets more requests to buy USD for Euros than Euros for USD, it adjusts the rate downwards until the buying pressure is even.  If the USD gets more expensive, at some point fewer people will want to buy it (or want to buy products from the US that cost USD).  The bank maintains a spread (like buy for 1.19 and sell for 1.21) so it can take a profit. You should think of currency like any other commodity, and consider purchases for currency as a form of barter.  The value of currency is merely a convention, but it works.  The currency is needed in transactions, so it maintains value in this global market of bartering goods/services and other currencies.  As supply and demand for this and other commodities/goods/services fluctuate, so does the quantity of any particular currency necessary to conduct any of these transactions. A official ""basket of goods"" and the price of those goods is used to determine consumer price indexes / inflation etc.  The official price of this particular basket of goods is not a fundamental driver of exchange rates on a day to day basis."

negative: "You will make a profit in nominal dollars (or nominal units of whatever currency you used to buy the token).  Whether you'll make a profit in real dollars depends on inflation, and in practice whether it would be possible to sell your existing tokens to someone else for the new price. Suppose when the price was 50 U (50 ""units"", since you didn't specify a currency), you bought one token.  Today you can either spend 52 U for a token, and get a liter of milk, or you can spend your existing token (for which you paid 50 U) and get a liter of milk.  It looks like you are making a profit of 2 U by spending your token. However, whether that profit is real or illusory depends on what else you could do with the token.  For instance, suppose that, since the price of a token is now 52 U, you will have no trouble finding someone who wants to buy your token from you for 52 U.  If you sell your token for 52 U, you'll still only be able to buy 1 L of milk.  So if you measure your wealth in milk, you have made no profit: in the past you had a token representing 1 L of milk, and today you still have a token representing 1 L of milk. Suppose now that in the past, when a token cost 50 U, a hamburger also cost 50 U.  Suppose further that a hamburger now costs 52 U.  So you can sell your token for 52 U, but that 52 U will still only buy you one hamburger.  So, again, if you measure your wealth in hamburgers, your have made no profit.  In the past, you could have sold your token and bought a hamburger; today, you can still sell your token and buy a hamburger, and you'll have nothing left over, so you have gained nothing. If, on the other hand, the price of a hamburger today is still 50 U, then you call sell your token for 52 U, buy a hamburger for 50 U, and still have 2 U left over.  You have made a profit. What this all goes to show is that, in practice, the idea of ""profit"" depends on the overall economy, and whether you could exchange the currency units you have in your possession for a greater quantity of goods than you could in the past.  Whether this is possible depends on the relative changes in price of various goods.  In other words, if you get your money by selling Product A, and later you buy Product B, you may or may not make a profit depending on how the prices of the two products moved relative to one another. Also, in your hypothetical setup, the ""currency"" (the token) is directly linked to the value of a single good, so you can always at least get 1 L of milk for your token.  Most real currency is not bound to specific goods like your milk token, so it is possible for your currency to lose value in an absolute sense.  For instance, suppose you sell a book for $5.  The $5 is not a ""book token"" and you cannot rely on being able to exchange it for a book in the future; in the future, all books may cost $10, and the prices of all goods may rise similarly, so your currency will actually be worth less no matter how you try to use it.  This could happen with the milk token if the milkman announces that henceforth 1 L of milk will cost 2 tokens; your existing token suddenly loses half its value. In sum, it is easy to calculate whether you made a profit in currency units.  What is harder is to calculate whether you made a profit in ""real terms"" (often referred to as ""real dollars"" or ""inflation-adjusted dollars"", or the equivalent in your favorite currency).  The reason this is hard is because the idea of ""real dollars"" is fundamentally linked to the possibility of exchanging currency for goods (and services), and so it depends what goods you're buying.  Inflation statistics published by governments and the like use a ""basket"" of goods to approximate the overall price movements in the economy as a whole."

negative: Just a thought because this is a really good question: Would the buying and selling of blockchain based digital currency,   using other blockchain based digital currencies, be subject to like   kind treatment and exempt from capital gains until exchanged for a   non-blockchain based good or service (or national currency) Suppose someone sells 1 bitcoin to buy 100 monero.  Monero's price and bitcoin's price then change to where the 100 monero are 3 bitcoins.  The person gets their bitcoin back and has 66.67 monero remaining. This scenario could be: Suppose someone sells 1 bitcoin at $1000 to buy 100 monero at $10.  Bitcoin crashes 80% to $200 while monero crashes to only $6 per monero.  $6 times 100 is $600 and if the person gets their bitcoin back (at $200 per bitcoi), they still lost money when measured in US Dollars if they move that bitcoin back to US dollars. In reading the IRS on bitcoin, they only care about the US dollar value of bitcoin or monero and in this example, the US dollar value is less.  The person may have more bitcoins, but they still lost money if they sell.

negative: The strategy could conceivably work if you had sufficient quantity of shares to fill all of the outstanding buy orders and fill your lower buy orders.  But in this case you are forcing the market down by selling and reinforcing the notion that there is a sell off by filling ever lower buy orders.  There is the potential to trigger some stop loss orders if you can pressure it low enough.  There is a lot of risk here that someone sees what you are doing and decides to jump in and buy forcing the price back up.  Could this work sure.  But it is very risky and if you fail to create the panic selling then you risk losing big.  I also suspect that this would violate SEC Rules and several laws.  And if the price drops too far then trading on the stock would be halted and is likely to return at the appropriate price. Bottom line I can not see a scenario where you do not trigger the stop, net a profit and end up with as many or more stock that you had in the first place.

negative: "Of the two, an option is a more reliable but more expensive means to get rid of a stock. As sdg said, a put option is basically an insurance policy on the stock; you pay a certain price for the contract itself, which locks in a sale price up to a particular future date. If the stock depreciates significantly, you exercise the option and get the contract price; otherwise you let the contract expire and keep the stock. Long-term, these are bad bets as each expired contract will offset earnings, but if you foresee a near-term steep drop in the stock price but aren't quite sure, a put option is good peace of mind. A sell stop order is generally cheaper, but less reliable. You set a trigger price, say a loss of 10% of the stock's current value. If that threshold is reached, the stop order becomes a sell order and the broker will sell the stock on the market, take his commission (or a fixed price depending on your broker) and you get the rest. However, there has to be a buyer willing to buy at that price at the moment the trigger fires; if a stock has lost 10% rapidly, it's probably on the way down hard, and the order might not complete until you realize a 12% loss, or a 15%, or even 20%. A sell stop limit (a combination stop order and limit order) allows you to say that you want to sell if the stock drops to $X, but not sell if it drops below $X-Y. This allows you to limit realized losses by determining a band within which it should be sold, and not to sell above or below that price. These are cheaper because you only pay for the order if it is executed successfully; if you never need it, it's free (or very cheap; some brokers will charge a token service fee to maintain a stop or stop limit). However, if the price drops very quickly or you specify too narrow a band, the stock can drop through that band too quickly to execute the sell order and you end up with a severely depreciated stock and an unexercised order. This can happen if the company whose stock you own buys another company; VERY quickly, both stocks will adjust, the buying company will often plummet inside a few seconds after news of the merger is announced, based on the steep drop in working capital and/or the infusion of a large amount of new stock in the buying company to cover the equity of the purchased company. You end up with devalued stock and a worthless option (but one company buying another is not usually reason to sell; if the purchase is a good idea, their stock will recover). Another option which may be useful to you is a swaption; this basically amounts to buying a put option on one financial instrument and a call on another, rolled into one option contract specifying a swap. This allows you to pick something you think would rise if your stock fell and exchange your stock for it at your option. For example, say the stock on which you buy this swaption is an airline stock, and you contract the option to swap for oil. If oil surges, the airline's stock will tank sharply, and you win both ways (avoiding loss and realizing a gain). You'd also win if either half of this option realized a gain over the option price; oil could surge or the airline could tank and you could win. You could even do this ""naked"" since its your option; if the airline's stock tanks, you buy it at the crashed price to exercise the option and then do so. The downside is a higher option cost; the seller will be no fool, so if your position appears to be likely, anyone who'd bet against you by selling you this option will want a pretty high return."

negative: "Most of the investors who have large holdings in a particular stock have pretty good exit strategies for those positions to ensure they are getting the best price they can by selling gradually into the volume over time. Putting a single large block of stock up for sale is problematic for one simple reason: Let's say you have 100,000 shares of a stock, and for some reason you decide today is the day to sell them, take your profits, and ride off into the sunset.  So you call your broker (or log into your brokerage account) and put them up for sale.  He puts in an order somewhere, the stock is sold, and your account is credited. Seems simple, right?  Well...not so fast. Professionals - I'm keeping this simple, so please don't beat me up for it! The way stocks are bought and sold is through companies known as ""market makers"".  These are entities which sit between the markets and you (and your broker), and when you want to buy or sell a stock, most of the time the order is ultimately handled somewhere along the line by a market maker.  If you work with a large brokerage firm, sometimes they'll buy or sell your shares out of their own accounts, but that's another story. It is normal for there to be many, sometimes hundreds, of market makers who are all trading in the same equity.  The bigger the stock, the more market makers it attracts.  They all compete with each other for business, and they make their money on the spread between what they buy stock from people selling for and what they can get for it selling it to people who want it. Given that there could be hundreds of market makers on a particular stock (Google, Apple, and Microsoft are good examples of having hundreds of market makers trading in their stocks), it is very competitive.  The way the makers compete is on price.  It might surprise you to know that it is the market makers, not the markets, that decide what a stock will buy or sell for. Each market maker sets their own prices for what they'll pay to buy from sellers for, and what they'll sell it to buyers for.  This is called, respectively, the ""bid"" and the ""ask"" prices.  So, if there are hundreds of market makers then there could be hundreds of different bid and ask prices on the same stock.  The prices you see for stocks are what are called the ""best bid and best ask"" prices.  What that means is, you are being shown the highest ""bid"" price (what you can sell your shares for) and the best ""ask"" price (what you can buy those shares for) because that's what is required.  That being said, there are many other market makers on the same stock whose bid prices are lower and ask prices are higher.  Many times there will be a big clump of market makers all at the same bid/ask, or within fractions of a cent of each other, all competing for business.  Trading computers are taught to seek out the best prices and the fastest trade fills they can. The point to this very simplistic lesson is that the market makers set the prices that shares trade at.  They adjust those prices based (among other factors) on how much buying and selling volume they're seeing.  If they see a wave of sell orders coming into the system then they'll start marking down their bid prices.  This keeps them from paying too much for shares they're going to have to find a buyer for eventually, and it can sometimes slow down the pace of selling as investors and automated systems notice the price decline and decide to wait to sell.  Conversely, if market makers see a wave of buy orders coming into the system, they'll start marking their ask prices up to maximize their gains, since they're selling you shares they bought from someone else, presumably at a lower price.  But they typically adjust their prices up or down before they actually fill trades.  (sneaky, eh?) Depending on how much volume there is on the shares of the company you're selling, and depending on whether there are more buyers than sellers at the moment, your share sell order may be filled at market by a market maker with no real consequence to the share's price. If the block is large enough then it's possible it will not all sell to one market maker, or it might not all happen in one transaction or even all at the same price. This is a pretty complex subject, as you can see, and I've cut a LOT of corners and oversimplified much to keep it comprehensible.  But the short answer to your question is -- it depends. Hope this helps. Good luck!"

negative: On expiry, with the underlying share price at $46, we have : You ask :  How come they substract 600-100. Why ? Because you have sold the $45 call to open you position, you must now buy it back to close your position.  This will cost you $100, so you are debited for $100 and this debit is being represented as a negative (subtracted); i.e., -$100 Because you have purchased the $40 call to open your position, you must now sell it to close your position.  Upon selling this option you will receive $600, so you are credited with $600 and this credit is represented as a positive (added) ; i.e., +$600. Therefore, upon settlement, closing your position will get you $600-$100 = $500.  This is the first point you are questioning.   (However, you should also note that this is the value of the spread at settlement and it does not include the costs of opening the spread position, which are given as $200, so you net profit is $500-$200 = $300.) You then comment :  I know I am selling 45 Call that means : As a writer: I want stock price to go down or stay at strike. As a buyer: I want stock price to go up. Here, note that for every penny that the underlying share price rises above $45, the money you will pay to buy back your short $45 call option will be offset by the money you will receive by selling the long $40 call option.  Your $40 call option is covering the losses on your short $45 call option. No matter how high the underlying price settles above $45, you will receive the same $500 net credit on settlement.  For example, if the underlying price settles at $50, then you will receive a credit of $1000 for selling your $40 call, but you will incur a debit of $500 against for buying back your short $45 call.  The net being $500 = $1000-$500.  This point is made in response to your comments posted under Dr. Jones answer.

negative: "I'm not sure the term actually has a clear meaning. We can think of ""what does this mean"" in two ways: its broad semantic/metaphorical meaning, and its mechanical ""what actual variables in the market represent this quantity"". Net buying/selling have a clear meaning in the former sense by analogy to the basic concept of supply and demand in equilibrium markets. It's not as clear what their meaning should be in the latter sense. Roughly, as the top comment notes, you could say that a price decrease is because of net selling at the previous price level, while a price rise is driven by net buying at the previous price level. But in terms of actual market mechanics, the only way prices move is by matching of a buyer and a seller, so every market transaction inherently represents an instantaneous balance across the bid/ask spread. So then we could think about the notion of orders. Actual transactions only occur in balance, but there is a whole book of standing orders at various prices. So maybe we could use some measure of the volume at various price levels in each of the bid/ask books to decide some notion of net buying/selling. But again, actual transactions occur only when matched across the spread. If a significant order volume is added on one side or the other, but at a price far away from the bid/offer - far enough that an actual trade at that price is unlikely to occur - should that be included in the notion of net buying/selling? Presumably there is some price distance from the bid/offer where the orders don't matter for net buying/selling. I'm sure you'd find a lot of buyers for BRK.A at $1, but that's completely irrelevant to the notion of net buying/selling in BRK.A. Maybe the closest thing I can think of in terms of actual market mechanics is the comparative total volumes during the period that would still have been executed if forced to execute at the end of period price. Assuming that traders' valuations are fixed through the period in question, and trading occurs on the basis of fundamentals (which I know isn't a good assumption in practice, but the impact of price history upon future price is too complex for this analysis), we have two cases. If price falls, we can assume all buyers who executed above the last price in the period would have happily bought at the last price (saving money), while all sellers who executed below the last price in the period would also be happy to sell for more. The former will be larger than the latter. If the price rises, the reverse is true."

negative: "SELL -10 VERTICAL $IYR 100 AUG 09 32/34 CALL @.80 LMT 1) we are talking about options, these are a derivative product whose price is based on 6 variables. 2) options allow you to create risk out of thin air, and those risks come with shapes, and the only limit is your imagination (and how much your margin/borrowing costs are). Whereas a simple asset like the shares for $IYR only has a linear risk profile. stock goes up, you make money, stock goes down, you lose money, and that risk graph looks linear. a ""vertical"" has a nonlinear risk profile 3) a vertical is a type of ""spread"" that requires holding options that expire at the same time, but at different strike prices. 3b) This particular KIND of vertical is called a bear call spread (BCS). Since you are bearish (this makes money if the stock goes down, or stays in a very specific range) but are using calls which are a bullish options product. 4) -10 means you are selling the vertical. +10 means you are buying the vertical. A ""long"" vertical is initiated by buying an option closer to the money, and selling an option at a higher strike price. This would be +X A ""short"" vertical is initiated by selling an option closer to the money and buying an option at a higher strike price. The quantity would be -X 5) 32/34 stands for the strike prices. so you would be selling 10 call options at the 32 strike price, and buying 10 call options at the 34 strike price, both options expire in August 6) LMT stands for limit order, and $.80 is the limit order price that is desired. OPENING a vertical spread requires knowledge of options as well as how to send orders. MANAGING a vertical requires even more finesse, as you can ""leg-in"" and ""leg-out"" of spreads, without sending the entire order to the exchange floor at once. There is much to learn."

negative: "A ""market maker"" is someone that is contractually bound, by the exchange, to provide both bid and ask prices for a given volume (e.g. 5000 shares). A single market maker usually covers many stocks, and a single stock is usually covered by many market makers. The NYSE has ""specialists"" that are market makers that also performed a few other roles in the management of trading for a stock, and usually a single issue on the NYSE is covered by only one market maker.  Market makers are often middlemen between brokers (ignoring stuff like dark pools, and the fact that brokers will often trade stocks internally among their own clients before going to the exchange).  Historically, the market makers gave up buy/sell discretion in exchange for being the ""go-to guys"" for anyone wanting to trade in that stock. When you told your broker to buy a stock for you, he didn't hook you up with another retail investor; he went to the market maker. Market makers would also sometimes find investors willing to step in when more liquidity was needed for a security. They were like other floor traders; they hung out on the exchange floors and interacted with traders to buy and sell stocks. Traders came to them when they wanted to buy one of the specialist's issues. There was no public order book; just ticker tape and a quote. It was up to the market maker to maintain that order book.  Since they are effectively forbidden from being one-sided traders in a security, their profit comes from the bid-ask spread. Being the counter-party to almost every trade, they'd make profit from always selling above where they were buying. (Except when the price moved quickly -- the downside to this arrangement.) ""The spread goes to the market maker"" is just stating that the profit implicit in the spread gets consumed by the market maker. With the switch to ECNs, the role of the market maker has changed. For example, ForEx trading firms tend to act as market makers to their customers. On ECNs, the invisible, anonymous guy at the other end of most trades is often a market maker, still performing his traditional role. Yet brokers can interact directly with each other now, rather than relying on the market maker's book. With modern online investing and public order books, retail investors might even be trading directly with each other. Market makers are still out there; in part, they perform a service sold by an Exchange to the companies that choose to be listed on that exchange. That service has changed to helping tamp volatility during normal high-volatility periods (such as at open and close)."

negative: "Put Options for Kids: You have a big box of candy bars. You saved up your allowance to get a lot of them, so you could have one whenever you want one. But, you just saw a commercial on TV for a new toy coming out in one month. Your allowance alone won't buy it, and you want that toy more than you want the candy. So, you decide that you'll sell the candy to your friends at school to buy the toy. Now, you have a choice. You can sell the candy now, and put the money in your piggy bank to buy the toy later. Or, you can save the candy, and sell it in a month when you actually need the money to buy the toy. You know that if you sell all the candy you have today, you can get 50 cents a bar. That's not quite enough to buy the toy, but your allowance will cover the rest.  What you don't know is how much you might be able to sell the candy for in a month. You might be able to get 75 cents a bar. If you did, you could pay for the toy with just the money from the candy and even have some left over. But, you might only be able to sell them for 25 cents each, and you wouldn't have enough to buy the toy even with your allowance. You'd like to wait and see if you could get 75 cents each, but you don't want to risk getting only 25 cents each. So, you go to your father. He and his co-workers like these candy bars too, so he'd be willing to buy them all and sell them to his friends the way you're planning to do with yours. You ask for the option to sell him all the candy bars for 50 cents each in one month. If you find out you can get more for them at school, you want to be able to take that deal, but if you can't sell them for 50 cents at school, you'll sell them to your dad. Now, your dad knows that he could have the same problem selling the candy at 50 cents or more that you are afraid of. So, he offers a compromise. If you pay him $5 now, he'll agree to the deal. You figure that even without that $5, between your allowance and the candy money, you can still buy the toy. So, you take the deal.  In one month, you can offer the candy at school. If nobody will pay 50 cents, you can sell the candy to your dad when you get home, but if the kids at school will pay 50 cents or more, you can sell it all at school. Either way, you have enough money to buy the toy, and you can also choose which price to accept, but you had to pay your dad $5, and you can't get that back, so if it turns out that you can sell the candy at school for 50 cents, same as today, then because you paid the $5 you don't end up with as much as if you'd simply waited. In the financial market, this type of option is a ""put option"". Someone who owns something that's traded on the market, like a stock, can arrange to sell that stock to someone else at an agreed-on price, and the seller can additionally pay some money to the buyer up front for the option to not sell at that price. Now, if the stock market goes up, the seller lets the contract expire and sells his stock on the open market. If it goes down, he can exercise the option, and sell at the agreed-upon price to the buyer. If, however, the stock stays about the same, whether he chooses to sell or not, the money the seller paid for the option means he ends up with less than he would have if he hadn't bought the option. Call Options for Kids: Let's say that you see another ad on TV for another toy that you like, that was just released. You check the suggested retail price on the company's web site, and you see that if you save your allowance for the next month, you can buy it. But, in school the next day, everybody's talking about this toy, saying how they want one. Some already have enough money, others are saving up and will be able to get it before you can. You're afraid that because everyone else wants one, it'll drive up the price for them at the local store, so that your month's allowance will no longer buy the toy. So, you go to your dad again. You want to be able to use your allowance money for the next month to buy the new toy. You're willing to wait until you actually have the money saved up before you get the toy, but you need that toy in a month. So, you want your dad to buy one for you, and hold it until you can save up to buy it from him. But, you still want it both ways; if the price goes down in a month because the toy's not so new anymore and people don't want it, you don't want to spend your entire month's allowance buying the one from your dad; you just want to go to the store and buy one at the lower price. You'll pay him $5 for the trouble, right now, whether you buy the toy he got you or not. Your dad doesn't want to have a toy he's not using sitting around for a month, especially if you might not end up buying it from him, so he offers a different deal; In one month, if you still want it, he'll stop by the store on his way home and pick up the toy. You'll then reimburse him from the allowance you saved up; if it ends up costing less than a month's allowance, so be it, but if it costs more than that, you won't have to pay any more. This will only cost you $3, because it's easier for him. But, because he's not buying it now, there is a small chance that the item will be out of stock when he goes to buy it, and you'll have to wait until it's back in stock. You agree, on the condition that if you have to wait longer than a month for your toy, because he couldn't get one to sell you, he pays you back your $3 and knocks another $5 off the cost to buy the toy from him. The basic deal to buy something at an agreed price, with the option not to do so, is known as a ""call option"". Someone who wishes to buy some stocks, bonds or commodities at a future date can arrange a deal with someone who has what they want to buy them at a specific price. The buyer can then pay the seller for the option to not buy. The counter-offer Dad made, where he will buy the toy from the store at whatever price he can find it, then sell it to you for the agreed price, is known as a ""naked call"" in finance. It simply means that the seller, who is in this case offering the option to the buyer, doesn't actually have what they are agreeing to sell at the future date, and would have to buy it on the open market in order to turn around and sell it. This is typically done when the seller is confident that the price will go down, or won't go up by much, between now and the date of the contract. In those cases, either the buyer won't exercise the option and will just buy what they want on the open market, or they'll exercise the option, but the difference between what the seller is paying to buy the commodity on the market and what he's getting by selling it on contract is within the price he received for the option itself. If, however, the price of an item skyrockets, the seller now has to take a significant, real loss of money by buying something and then selling it for far less than he paid. If the item flat-out isn't available, the buyer is usually entitled to penalties for the seller's failure to deliver. If this is all understood by both parties, it can be thought of as a form of insurance."

negative: Basic arbitrage is the (near-)simultaneous purchasing and selling of things that are convertible.   The classic example is the international trading of equities. If someone in London wants to purchase a hundred shares of Shell for 40 GBP ea. and someone in New York wants to sell you a hundred shares of Shell for 61 USD ea., you can buy the shares from the guy in New York, sell them to the guy in London and convert your GBP back in to USD for a profit of $41.60 minus fees.  Now, if after you buy the shares in New York, the price in London goes down, you'll be left holding 100 shares of Shell that you don't want. So instead you should borrow 100 shares in London and sell them at the exact same time that you buy the shares in New York, thus keeping your net position at 0. In fact, you should also borrow 4000GBP and convert them to USD at the same time, so that exchange rate changes don't get you.

negative: "I have heard that investing more money into an investment which has gone down is generally a bad idea*. ""Throwing good money after bad"" so to speak. This is over simplified statement to explain the concept. What is essentially says is; Say I hold stocks of XYZ; 100 units worth say USD 1000. This has lost me x% [say 50%]. The general tendency is to buy 100 more units in anticipation / hope that the price will go up. This is incorrect.  However on case to case basis, this maybe the right decisions. On a periodic basis [or whenever you want to invest more money]; say you have USD 1000 and did not have the stock of XYZ, will you buy this at current price and outlook of the company. If the answer is Yes, hold the stock [or buy more], if the answer is no sell the stock at current market price and take the loss. The same applies when the price has appreciated. If you have USD 1000; given the current price and future outlook, will you buy the specific stock. If yes, hold the stock [or buy more], if answer is no sell the stock and book profit. Off-course I have not overlaid the various other considerations when buying stocks like diversification, risk profiles of individual stocks / segments, tax implications etc that are also essential even if you decide to buy or sell specific stock."

negative: Mutual funds are a collection of other assets, such as stocks, bonds and property. Unless the fund is a type that is traded on an exchange, you will only be able to buy into the fund by applying for units with the fund manager and sell out by contacting the fund manager. These type of non-traded funds are usually updated at the end of the day once the closing prices of all the assets in it are known.

negative: Step 1: Buy stock with own money   Step 2: Buy big block of same stock with clients' money, and push the price up   Step 3: Go on tv to encourage public to buy the same stock, to push price up even further   Step 4: Sell your holding, and profit   Step 5: Sell your clients' holding and profit from commission   Step 6: Keep low profile so public forgets your lame advice   Step 7: Repeat

negative: "Not all call options that have value at expiration, exercise by purchasing the security (or attempting to, with funds in your account).   On ETNs, they often (always?) settle in cash.  As an example of an option I'm currently looking at, AVSPY, it settles in cash (please confirm by reading the documentation on this set of options at http://www.nasdaqomxtrader.com/Micro.aspx?id=Alpha, but it is an example of this).  There's nothing it can settle into (as you can't purchase the AVSPY index, only options on it).  You may quickly look (wikipedia) at the difference between ""American Style"" options and ""European Style"" options, for more understanding here. Interestingly I just spoke to my broker about this subject for a trade execution.  Before I go into that, let me also quickly refer to Joe's answer:  what you buy, you can sell.  That's one of the jobs of a market maker, to provide liquidity in a market.  So, when you buy a stock, you can sell it.  When you buy an option, you can sell it.  That's at any time before expiration (although how close you do it before the closing bell on expiration Friday/Saturday is your discretion).  When a market maker lists an option price, they list a bid and an ask.  If you are willing to sell at the bid price, they need to purchase it (generally speaking).  That's why they put a spread between the bid and ask price, but that's another topic not related to your question -- just note the point of them buying at the bid price, and selling at the ask price -- that's what they're saying they'll do. Now, one major difference with options vs. stocks is that options are contracts. So, therefore, we can note just as easily that YOU can sell the option on something (particularly if you own either the underlying, or an option deeper in the money).  If you own the underlying instrument/stock, and you sell a CALL option on it, this is a strategy typically referred to as a covered call, considered a ""risk reduction"" strategy.  You forfeit (potential) gains on the upside, for money you receive in selling the option. The point of this discussion is, is simply: what one buys one can sell;  what one sells one can buy -- that's how a ""market"" is supposed to work.  And also, not to think that making money in options is buying first, then selling.  It may be selling, and either buying back or ideally that option expiring worthless. -- Now, a final example.  Let's say you buy a deep in the money call on a stock trading at $150, and you own the $100 calls.  At expiration, these have a value of $50.  But let's say, you don't have any money in your account, to take ownership of the underlying security (you have to come up with the additional $100 per share you are missing).  In that case, need to call  your broker and see how they handle it, and it will depend on the type of account you have (e.g. margin or not, IRA, etc).  Generally speaking though, the ""margin department"" makes these decisions, and they look through folks that have options on things that have value, and are expiring, and whether they have the funds in their account to absorb the security they are going to need to own.  Exchange-wise, options that have value at expiration, are exercised.  But what if the person who has the option, doesn't have the funds to own the whole stock? Well, ideally on Monday they'll buy all the shares with the options you have at the current price, and immediately liquidate the amount you can't afford to own, but they don't have to.  I'm mentioning this detail so that it helps you see what's going or needs to go on with exchanges and brokerages and individuals, so you have a broader picture."

negative: "Many people assume that if the price of something is $10 and they have 1,000 of that thing, they should expect to be able to sell them for something around $10,000.  Such an assumption may hold much of the time, but it doesn't always.  Worse, the cases where it fails to hold are often those where it would be relied upon most heavily.  Such an assumption should thus be considered dangerous. In a liquid market, the quantity of a something that people would be willing to buy at something close to the market price will be large relative to the quantity that people would seek to sell in the short term.  If at some moment in time one person in the market was willing to immediately buy 500 shares at $9.98 and another was willing to immediately buy 750 at $9.97, someone seeking to sell 1,000 shares could immediately receive $997.50 for them (selling 500 to the first person and 500 to the second, who would then be ready to buy 250 more from the first person who was willing to sell for $9.97).  Such behavior would be in line with what many people's assumptions. In an illiquid market, however, the quantity of something that people would be willing to buy near market price could be surprisingly low.  This is more often a problem in the marketplace of things like collectibles than of stocks, but the same thing can happen in the stock market.  If there's one potential buyer for a stock who thinks it's overpriced but has potential and would be worth $9.50, but that person only has $950 to spend, and nobody else thinks the stock would be worth more than $0.02/share, then until people sold a total of 100 shares the price would be $9.50, but after that the price would drop instantly to $0.02.  There would be no ""cushioning"" of the fall.  If the person with 1,000 shares was first in line, he'd get to sell 100 shares for $950 to the aforementioned seller, but would be unable to get more than $18 for the remaining 900. A major danger with markets is that markets which are perceived as liquid attract people to the buying side, while those which are seen as illiquid repel people.  The danger in the latter is obvious (having people flee a seemingly-illiquid market will reduce its liquidity further) but the former is just as bad.  Having people flock to a market because of its perceived liquidity will increase its liquidity, but can also create a ""false price floor"", causing demand to appear much stronger than it actually is.  Unless real demand increases to match the false price floor, the people who buy at the higher price will never be able to recoup their investment."

negative: "When you buy a put option, you're buying the right to sell stock at the ""strike"" price. To understand why you have to pay separately for that, consider the other side of the transaction. If I agree to trade stock for money at above market rates, I need to make up the difference somewhere or face bankruptcy.  That risk of loss is what the option price is about. You might assume that means the market expects the price of AMD to fall to 8.01 from it's current price of 8.06 by the option expiration date. But that would also mean call options below the market price is worthless. But that's not quite true; people who price options need to factor in volatility, since things change with time. The price MIGHT fall, and traders need to account for that risk. So 1.99 roughly represents the probability of AMD rising to 10. There's probably some technical analysis one can do to the chain, but I don't see any abnormality of AMD here."