Merger Control in a Changing World

How should merger control account for future changes in market conditions? We study horizontal merger policy in the presence of industry-wide cost or demand shocks, using both a homogeneous-goods Cournot model and a multiproduct-firm model of price competition with constant elasticity of substitution (CES) or multinomial logit (MNL) demand. We derive two main sets of results. First, regarding deterministic shocks: under both Cournot competition with incomplete pass-through and multiproduct firm price competition, an adverse shock increases industry concentration but calls for softer merger control. Second, regarding cost or demand uncertainty: under a cautious maxmin approach, aggregate cost uncertainty calls for softer merger control under the same assumptions. By contrast, under a risk-neutral expected-consumer-surplus stan dard, greater cost uncertainty demands tougher merger control in the Cournot model with log-concave demand, and in the multiproduct-firm price competition model when the outside option is sufficiently attractive.