Oxidative behavior of commercial engineering plastics, polyolefins and elastomers has been evaluated by simultaneous thermogravimetric analysis (TGA)-differential thermal analysis (DTA) and pressure differential scanning calorimetry (PDSC). There is a good correlation between the measured stability by PDSC in oxygen and DTA/TGA in air and nitrogen for olefin polymers. The thermo-oxidative properties of engineering plastics, polyolefins and elastomers are reliable and precise. Glass-filled Nylon 66 and reinforced polypropylene were studied in an air oven at 300 degrees C as a function of time by Fourier transform infrared (FTIR) spectroscopy. The mechanism for thermal oxidation was different for these two polymers. Polyolefin oxidation was delineated by rapid carbonyl formation, while Nylon 66 showed minimum carbonyl in the FTIR. An interesting outcome of this study is that polyethylene and polypropylene have significantly high heats of combustion. At high temperatures and pressures, it appears that these polymers can be used as sources of fuel.