Information advantage and dominant strategies in second-price auctions

We study a general model of common-value second-price auctions with differential information. We show that one of the bidders has an information advantage over the other bidders if and only if he possesses a dominant strategy. A dominant strategy is, in fact, unique, and is given by the conditional expectation of the common value with respect to his information field. Furthermore, when a bidder has information advantage, other bidders cannot make a profit.