Jeroen Swinkels Northwestern University SBR-9507894 The P.I. proposes to explore the equilibrium behavior of auctions when the number of participants is large. The motivation for this research program is the restrictiveness of the assumptions required to ensure that auction outcomes are efficient: a single unit for sale for a single period, symmetry of bidder preferences and beliefs, and risk neutrality of bidders. The P.I. conjectures that efficiency is recovered if the number of players becomes large enough and has already obtained such a result for the single-unit, independent value case with asymmetric risk-nuetral bidders. The proposal is to extend this to auctions with multiple units, multiple periods, multidimensional signals, and risk averse bidders.