This paper focuses on the effect of merger on university efficiency. In a first stage analysis, efficiency scores of English universities are derived for a 17-year period using the frontier estimation method data envelopment analysis. A second stage analysis explores the effect of merger and other factors on efficiency. We find that mean efficiency for the sector has varied from around 60% to 70%, but that the efficiency levels of the vast majority of individual higher education institutions (HEIs) are not significantly different from each other. Merged HEIs have an efficiency which is around five percentage points higher post-merger than non-merging HEIs holding all else constant; but we find that the efficiency impact of merger does not last long (not more than a year) after the merger. The transitory nature of the efficiency gain is an important finding which should be noted by politicians and managers considering a policy of merger.