Evolution of the Merger Guidelines: Is This Fox Too Clever by Half?

Abstract The 2023 Merger Guidelines make some notable improvements over the 2010 Horizontal Merger Guidelines. They give greater emphasis to the idea that predicting the competitive effects of a proposed merger is inherently difficult and that to block a merger the government need only show a risk that the merger may substantially lessen competition – not that it will do so. They also give greater emphasis to dynamic competition and innovation – especially with regard to acquisitions of potential entrants – and they add useful material on multi-sided platforms. However, the treatment of market definition in the 2023 Merger Guidelines may weaken horizontal merger enforcement by demoting the role of the “hypothetical monopolist test,” which is used to define markets for the purpose of measuring market shares, and by removing extensive material from prior guidelines that explained why market shares measured in narrower markets tend to be more informative than market shares measured in broader markets. The 2023 Merger Guidelines lower the market concentration thresholds that trigger a presumption by the antitrust enforcement agencies that a merger may substantially lessen competition, but the enforcement data suggest that change will have little effect in practice. The 2023 Merger Guidelines also may lead to less effective deterrence of harmful mergers because they are not well targeted at the mergers that are most likely to substantially lessen competition. One cannot prioritize everything.