MarkHutch - 4:47 am on Nov 6, 2005 (gmt 0)

It's probably smart pricing and the amounts that adverstisers are bidding on keywords. Bid are real time and just because someone is bidding 50 cents for a certain keyword right now, doesn't mean they will still be bidding that amount an hour from now. The top bid might be 50 cents and the next bid only 15.