Bribing in second-price auctions

An IPV 2-bidder second-price auction is preceded by two rounds of bribing: prior to the auction each bidder can try to bribe his rival to depart from the auction, so that he (the briber) will become the sole participant and obtain the good for the reserve price. Bribes are offered sequentially according to an exogenously given order—there is a first mover and a second mover. I characterize the unique efficient collusive equilibrium in monotonic strategies; in it, the second mover extracts the entire collusive gain. This equilibrium remains an equilibrium even when valuations are interdependent, and if they are separable then the full surplus extraction result continues to hold. Additionally, a family of pooling equilibria is studied, in which all the types of the first mover offer the same bribe.