Abstract: Sponsored search is a new online marketing method that achieves great success in recent years.In this paper,we analyze different auction mechanisms used by search engines,and present the bidding behaviors of advertisers in the condition that quality score is implemented.We first examine a single period and simultaneous move game,and show that in this game,both advertisers choose their best strategies without considering their opponents policy.Then,we consider a multi-period game.In this game,we provide and prove an optimal strategy for advertisers given their opponent using a minimum out bidding strategy.The proposed strategy is verified by empirical data.Besides,we propose three related corollaries that are meaning ful to search engines.

Key words: sponsored search, GSP auction, competitive analysis, quality score