Objective. Cesarean section can be a lifesaving procedure. However, as with many surgeries, it is not exempt of complications. Surgical site infections generate higher costs, serious morbidity, and mortality. This study evaluates the benefits of perioperative oxygen to prevent surgical site infections. Methods. We conducted a randomized controlled trial to assess the effects of perioperative oxygen to prevent surgical site infection after emergency cesarean section. Patients were randomized to receive either oxygen (80% FIO 2 ) during cesarean section plus two hours postsurgery or no supplemental oxygen. A sample of 326 patients was calculated for the primary outcome (163 in each group) and they were evaluated daily before leaving the hospital, at days 15 and 30. Results. Initially, 360 patients were enrolled, from which 17 were excluded (sample size: 343 (179 patients in the air group and 164 in the oxygen group)). We found no significant difference in the incidence of surgical site infection between these two groups at any of the evaluation times. Conclusion. In this study of patients with emergency cesarean section, we showed that the use of supplemental oxygen does not reduce the incidence of surgical site infection. This trial is registeres with ClinicalTrials.gov NCT01340534.