An understanding of bank branch efficiency may help resolve a number of conceptual, measurement, and policy questions about efficiency at the bank level. We measure the efficiency of over 760 branches of a large U.S. commercial bank. We find that there are about twice as many branches as would minimize costs, but this may be optimal from a profitability standpoint because ‘overbranching’ raises revenues from providing extra customer convenience. X-inefficiencies are quite large, over 20% of operating costs. These findings may help explain some efficiency results commonly found in bank-level analysis, and have important implications regarding bank M&As and interstate branching.