Dynamic Merger Review

We analyze the optimal dynamic policy of an antitrust authority toward horizontal mergers when merger proposals are endogenous and occur over time. Approving a currently proposed merger may affect the profitability and welfare effects of potential future mergers, whose characteristics may not yet be known. We identify conditions under which discounted expected consumer surplus is maximized by using a completely myopic merger review policy that approves a merger if and only if it does not lower consumer surplus given the current market structure. We also discuss a number of extensions as well as factors that undermine the optimality of myopic merger review policies.