Despite its near-universal use, few data exist to support the efficacy of prehospital supplemental oxygen (PH O2) in trauma patients. Data were reviewed from 5,090 patients not requiring assisted ventilation who were transported to our level I trauma center. Of these, 2,203 (43.3%) received PH O2 and 2,887 (56.7%) did not. Patients who received PH O2 had higher mortality than those without PH O2 (2.3% vs. 1.1%, p = 0.011). When corrected for Injury Severity Score, mechanism of injury, and age, those receiving PH O2 fared worse or no better than those who did not receive it. This suggests that supplemental oxygen does not improve survival in traumatized patients who are not in respiratory distress. This has implications for the management of casualties in combat or austere environments.