Judicial Response to the 2010 Horizontal Merger Guidelines

We study how the courts have responded to the 2010 Horizontal Merger Guidelines issued by the U.S. Department of Justice and the Federal Trade Commission. Looking at decided cases, we find that both the government and merging parties rely on the 2010 Guidelines in presenting their cases, each side respectively arguing that it should win if the court properly follows them. The 2010 Guidelines had the strongest effect on the case law in the area of unilateral effects, where a number of courts have embraced them in ways that clearly depart from earlier decisions. The case law now exhibits much greater receptivity to a government showing that the merger will lead to higher prices simply due to the loss of direct competition between the two merging firms. The courts also have followed the 2010 Guidelines by more willingly defining markets around targeted customers. We do not detect any effect on decided cases of the higher concentration thresholds found in the 2010 Guidelines. Both the average pre-merger level of market concentration and the average increase in market concentration alleged by the government in litigated cases to date declined after 2010