We analyse all final merger decisions by the European Commission from 1990 to 2019 with a novel dataset, containing information about 6245 merger cases from all economic sectors and combining all types of decisions, including withdrawn and prohibited cases. Using text analysis techniques such as a keyness analysis and a dictionary approach, we find that terms associated with the More Economic Approach (MEA) are used increasingly, whereas the concept of dominance has decreased since 2004. The tonality of decision documents is predominantly positive, especially for cleared cases, and shows variation under different merger regulatory frameworks. Accounting for differences in the usage of competition-related terms and by using ordinary least squares and logit regressions, we find that the impact of the 2004 merger regulation, the 2007 guidelines for non-horizontal mergers, and the 2013 merger simplification package on the duration of investigations is evident in terms of procedural duration. While the 2004 merger regulation has extended the
review period, the subsequent guidelines have shortened it. Changes in the probability of prohibition are minor, likely within one percentage point.