Revenue effects of ambiguity in multi-unit auctions

We study the effect of ambiguity on expected revenue in multi-unit auctions where bidders have independent private values, maxmin preferences, and single-unit demand. If the set of priors is suitably rich, we show that the discriminatory or ‘pay-as-bid’ auction has the highest expected revenue, followed by the sequential first-price auction and then the sequential second-price auction. The uniform price auction with the ‘highest losing bid’ pricing rule does the worst. Our results also extend to some open auction formats.