varying willingness to pay is market segmentation. A firm may repackage its basic inventory into different products to this end. In the passenger airline case this means implementing purchase restrictions, length of stay requirements and requiring fees for changing or canceling tickets. The airline needs to keep a specific number of seats in reserve to cater to the probable demand for high-fare seats. This process can be managed by inventory controls or by managing the fare rules such as the AP (Advanced Purchase) restrictions. (30 day advance purchase, 21 day advance purchase, 14 day advance purchase, 7 day advance purchase, day of departure/walk up fares) The price of each seat varies directly with the number of seats reserved, that is, the fewer seats that are reserved for a particular category, the lower the price of each seat. This will continue until the price of seat in the premium class equals that of those in the concession class. Depending on this, a floor price (lower price) for the next seat to be sold is set. Hotels Hotels use this system in largely the same way, to calculate the rates. Yield management is one of the most common pricing strategies used in the hotel industry to increase reservations and boost revenue. Rental In the rental car industry, yield management deals with the sale of optional insurance, damage waivers and vehicle upgrades. It accounts for a major portion of the rental company's profitability, and is monitored on a daily basis. In the equipment rental industry, yield management is a method to manage rental rates against capacity (available fleet) and demand. Intercity buses Yield management has moved into the bus industry with companies such as Megabus (United Kingdom), Megabus (North America), BoltBus, and easyBus, which run low-cost networks in the United Kingdom and parts of the United States, and more recently, nakedbus.com and Intercape, which have networks in New Zealand and South Africa. Now operating and developed in Chile by SARCAN, a Chilean company that provides revenue and yield management systems focused on this industry, with the company Turbus as principal customer. Finnish low-cost inter-city bus service OnniBus, as well as Polish PolskiBus, bases its revenue flow on yield management. Multifamily housing In the multi-family residential industry, yield optimization is focused on producing supply and demand forecasts to determine rent recommendations for profit optimization. However, the use of the yield optimization systems is fairly