Merger control impacts the type of merger projects that are submitted, as well as the information provided by the merging parties upon assessment. In this paper, we consider the outcomes in terms of selection of merger types and evidence provision of alternative timings for merger review, pre‐ or postconsummation of the merger. We show that the selection effect induced by the ex post merger review is welfare‐improving due to the deterrence of the most anticompetitive merger projects. In contrast, the welfare impact of evidence provision under ex post assessment is ambiguous. Balancing these two effects makes possible the welfare comparison between the ex ante and the ex post merger policy enforcement.