Pay-as-bid Auctions with Private Information

Abstract

The pay-as-bid auction is one of the most prominent mechanisms allocating divisible goods like energy. This paper analyzes equilibrium behavior in pay-as-bid auctions within a general environment where bidders are privately informed about their valuations. The key methodological innovation is to represent the auction as a continuum of asymmetric first-price auctions. I define an everywhere-optimal Bayes-Nash equilibrium, in which bid functions satisfy pointwise optimality, and characterize equilibrium strategies. With two bidders, I establish equilibrium uniqueness. The characterization enables accurate predictions of equilibrium bids even when estimated valuations contain small errors. For a class of linear marginal valuations, I derive closed-form solutions and show that pay-as-bid generates higher revenue than the VCG mechanism.