Ordered Advantage for Cats over 9 pounds in the 6 pack size.  Amazon had the best price I could find.  Bayer makes this product which is very effective for immediately kills adult fleas (as opposed to othe products that only kill the eggs).  However, it appears that Bayer has, and continues, to spend a lot of time and resources to make sure that no one any where sells this product below a certain price they want which I've documented going up every month and is rapidly approaching $10 a month per treatment (per cat).  I have 5 rescued cats so the price adds up to $50 per month to treat them for fleas.  Every source I could find that sold this product at bargin prices has been forced to cease selling it.  This use to be called price fixing.  Nevertheless, the product works very well.  As soon as I can find another product that will kill adult fleas for less money than the outrageous price of Bayer's Advantage, I will switch.  My order arrived very fast and was well packaged.  I will use this merchant again.  The 5 star rating is for the retail merchant, Amazon and the effectiveness of the product.