The main goal of this paper is to empirically test the function of European merger control in light of the 2004 regulatory reform, which was expected to introduce a more efficient regulatory framework for the assessment of mergers within the EU. We use stock market data to identify cases where there are discrepancies between the European Commission’s decisions compared to market evaluations of the mergers in question. Using the PROBIT model, these cases are further investigated to discover the sources of these discrepancies. In line with previous studies, our results suggest that the discrepancies are caused by procedural and institutional factors. Nevertheless, the regulatory reform introduced in 2004 has, to some extent, enhanced the effi...