The recent banking literature has evaluated the impact of mergers on the efficiency of the merging parties [e.g., Rhoades (1993), Shaffer (1993), Fixler and Zieschang (1993)]. Similarly, there has been analysis of the impact of eliminating bank entry restrictions on the average performance of banks [Jayaratne and Strahan (1998)]. The evidence suggests that acquiring banks are typically more efficient than are acquired banks, resulting in the potential for the new combined organization to be more efficient and, therefore, for the merger to be welfare enhancing. The evidence also suggests, however, that these potential gains are often not realized. This has led some to question the benefits resulting from the recent increase in bank merger activity. We take a somewhat more comprehensive and micro-oriented approach and evaluate the impact of actual and potential competition resulting from market-entry mergers and reductions in entry barriers on bank efficiency. In particular, in addition to the efficiency gains realized by the parties involved in a bank merger, economic theory argues that additional efficiency gains should result from the impact of the merger on the degree of local market competition. We therefore examine the impact of increased competition resulting from mergers and acquisitions on the productive efficiency of incumbent banks. Our findings are consistent with economic theory: as competition increases as a result of entry or the creation of a more viable local competitor, the incumbent banks respond by increasing their level of cost efficiency. We find this efficiency increase to be in addition to any efficiency gains resulting from increases in potential competition occurring with the initial elimination of certain entry barriers. Thus, consistent with economic theory, new entrants and reductions in entry barriers lead incumbent firms to increase their productive efficiency to enable them to be viable in the more competitive environment. Studies evaluating the impact of bank mergers on the efficiency of the combining parties alone may be overlooking the most significant welfare enhancing aspect of merger activity. We do not find evidence of profit efficiency gains. In fact, the mergers are associated with decreases in profit efficiency; perhaps indicating that revenues may also be competed away from incumbents as a result of mergers.