Installation of power makeup equipment (PME) on 13 of 30 mobile offshore drilling units (MODUs) under study in the Gulf of Mexico provided an opportunity to evaluate the effectiveness of this device in reducing drill floor injuries. Two groups of injuries were defined on the basis of worker activity at the time of injury and the vehicle of mechanical energy; one group, "related" injuries, were preventable by the PME; the other group, "unrelated" injuries, should not have been affected by the PME. Two quasiexperimental evaluation designs were employed. The first, a multiple time series comparison of MODUs equipped and not equipped with PME, yielded a quantitative estimate of injuries averted. The second, a pretest-posttest design, compared related and unrelated injuries before and after PME installation. Because this method was subject to bias if different trends were present for related and unrelated injuries, only qualitative results could be obtained. Both methods indicated a significant reduction in related injuries attributable to the PME. A cost-savings analysis indicated savings that could conservatively pay for the equipment within six years time.