This paper presents a retrospective case study of merger efficiencies in the context of the merger of the Union Pacific Railroad Co. and the Southern Pacific Transportation Co., as approved by the Surface Transportation Board in 1996. There is sufficient information on the public record to permit some evaluation of merging parties' pre-merger efficiency claims, and to weigh these claims against regulatory and antitrust standards. The author also had access to public and certain normally non-public sources of information sufficient to permit at least a preliminary assessment of the extent to which claimed efficiencies were actually realized post-merger. Contrary to skepticism expressed about merger efficiency claims, both generally and with respect to this particular rail merger, a variety of available evidence suggests that a number of the claimed efficiencies were plausibly merger-specific and were actually realized post-merger.