An Efficient Ascending-Bid Auction for Multiple Objects: Comment

Ausubel (2004) introduces a new ascending-bid auction rule for multiple homogeneous objects, called the Ausubel auction, which is a dynamic counterpart of the Vickrey auction. He claims that in the Ausubel auction with private values, sincere bidding by all bidders is an ex post perfect equilibrium. However, we show that this claim does not hold in general by providing a counterexample. We then modify the Ausubel auction so that sincere bidding by all bidders is an ex post perfect equilibrium.