Buyers’ welfare maximizing auction design

I derive the incentive compatible and individually rational mechanism that maximizes the sum of the buyers’ ex-ante expected utilities. I also show that this mechanism minimizes the seller’s revenue. When payments are required to be non-negative, my mechanism takes the form of an arbitrarily weighted lottery with no participation fees, and the resulting allocation is generally not ex-post efficient. This means that before learning their valuations and if side payments from the seller to the buyers are not allowed, buyers as a group would be better off if they gave up ex-post efficiency in order to avoid positive payments. When transfers are allowed, the optimal mechanism is a standard auction with no reserve price and where the seller’s income is redistributed back to the buyers. This mechanism is robust to speculators if a buyer with value 0 never partakes in the redistribution.