Mergers that substantially lessen competition are challenged by antitrust authorities. Instead of blocking anticompetitive transitions straight away, authorities might choose to negotiate with the merging parties and allow the transactions to proceed with modifications that restore or preserve the competition in the involved markets. We study a sample of 167 mergers that were under the European Commission’s scrutiny from 1990 to 2002. We use an event study methodology to identify the potential anticompetitive effects of mergers as well as the remedial provisions on these transactions. Stock market reactions around the day of the merger’s announcement provide information on the first question, whereas the stock market reactions around the co...