Collusion via signaling in open ascending auctions with multiple objects and complementarities

Collusive equilibria exist in open ascending auctions with multiple objects, if the number of bidders is sufficiently small relative to the number of objects, even with large complementarities in the buyers' utility functions. The bidders collude by dividing the objects among themselves, while keeping the prices low. Hence the complementarities are not realized

Merger Mechanisms

A firm can merge with one of n potential partners. The owner of each firm has private information about both his firm’s stand-alone value and a component of the synergies that would be realized by the merger involving his firm. We characterize incentive-efficient mechanisms in two cases. First, we assume that the value of any newly formed partnership is verifiable, hence transfers can be made contingent on the new information accruing after the merger. Second, we study the case of uncontingent rules. In the first case, we show that it is not optimal, in general, to redistribute shares of non-merging firms, and identify necessary and sufficient conditions for the implementability of efficient merger rules. In the second case, we show that the first-best can be obtained i) always, if the synergy values are privately known but the firms’ stand-alone values are observable; ii) only with sufficiently large synergies, if the firms’ stand-alone are privately known; and iii) never, if the set of feasible mechanisms is restricted to “auctions in shares”.Mechanism design, Merger

Merger Mechanisms

A firm can merge with one of n potential partners. The owner of each firm has private information about both his firm's stand-alone value and a component of the synergies that would be realized by the merger involving his firm. We characterize incentive-efficient mechanisms in two cases. First, we assume that the value of any newly formed partnership is verifiable, hence transfers can be made contingent on the new information accruing after the merger. Second, we study the case of uncontingent rules. In the first case, we show that it is not optimal, in general, to redistribute shares of non-merging firms, and identify necessary and sufficient conditions for the implementability of efficient merger rules. In the second case, we show that the first-best can be obtained i) always, if the synergy values are privately known but the firms' stand-alone values are observable; ii) only with sufficiently large synergies, if the firms' stand-alone are privately known; and iii) never, if the set of feasible mechanisms is restricted to "auctions in shares".

Simultaneous Ascending Bid Auctions with Budget Constraints

We identify and analyze three distinct effects arising from potentially binding budget constraints in multi-unit ascending auctions. First, binding budgets clearly reduce the level of competition among bidders. Second, budget constraints may at the same time make it difficult to sustain collusive equilibria when bidders lack sufficient resources to ‘punish’ defectors. Third, the mere possibility, even if arbitrarily small, of binding budget constraints can reduce competition substantially because bidders can ‘pretend’ to be constrained, even if they are not. In this cases, measures restricting the participation of low-budget bidders, e.g. reserve prices, can increase social welfare