Thin films (0.05–0.08 mm thick) of stabilized and unstabilized polypropylene were aged under 4.24 MPa (614 psi) of oxygen at 90°C. The oxidation of these films was monitored using transmission infrared spectroscopy. Previously it was shown that embrittlement for the thin unstabilized polypropylene films occurred 3.6 times faster in 4.24 MPa of oxygen than in air at atmospheric pressure. For thick stabilized polypropylene (3.18 mm thick), the oxidative induction time at 120°C and 4.24 MPa of oxygen was drastically reduced compared with conventional air aging at this temperature. Specifically, sample embrittlement occured in 1 week during the high oxygen pressure aging in stark contrast to 70 weeks for conventional air aging. Consequently, due to the shortening of time to age samples at high oxygen pressures, aging can be conducted at this lower temperature (nearer the service temperature) rather than at this commonly used aging temperature of 150°C.