Abstract As part of the NASA High Speed Research Program and as a continuation of a test program developed at Boeing — Long Beach [Tsotsis TK, Keller S, Lee K, Bardis J, Bish J. 3000 hours aging of polymeric composite specimens under elevated presssure and temperature. Presented at 44th International SAMPE Symposium 24–27 May, 1999 (closed paper). Tsotsis TK, Keller S, Bardis J, Bish J. Preliminary examination of the use of elevated pressure to accelerate thermo-oxidative aging in composites. Polym Degrad Stab 1999;64:207–12.], the effects of elevated pressures in conjunction with elevated temperatures on the thermo-oxidative stability of polymeric composites are being investigated. This test program examines four different air pressures — 0.101, 0.345, 1.03, and 1.72 MPa (14.7, 50, 150, and 250 psi)—for carbon/epoxy specimens aged at 121°C (250°F) for up to 5000 h. Specimens used were AS4/3501-6 [±45°]2s tensile shear and IM7/8552 [+45°/0°/−45°/90°] 2s open-hole compression. The materials used were selected to evaluate the test method and not as candidate materials for use at higher temperatures. The test results show a distinct accelerating effect with the use of elevated pressures especially for the tensile shear coupons. The results also suggest that elevated pressure may be a good tool for significantly reducing screening times for material that will be subjected to long exposures in oxygen-containing environments at elevated temperatures.