Abstract: For an online English auction on eBay, this paper presents the expressions for the seller's expected revenue with or without the reserve price, and finds that the total number of bidders and the absolute difference between the upper bound and the lower bound of bidders' valuation are compensated with each other on the expected revenue. It is shown that the expected revenues are concave and strictly increase at the compensating rate, and that when bidders are enouth the maximum expected revenues almost remain the same whether or not the reserve price is set.

Key words: online auction, reserve price, starting price