The oxidation of polybenzimidazolone and selected model compounds including compounds containing benzimidazole and benzimide ring systems has been investigated at temperatures from ambient to 700°C. Residue elemental analyses, volatile product distribution differences as a function of time and oxidation temperature, thermogravimetry, and differential thermal analysis studies are reported. The determination of the energy of activation for the over-all initial oxidation processes over the ranges of 0 to 15% weight loss and 100 to 700°C indicated a value of 35.5 kcal/mole. The elemental analyses data indicate that significant differences in residue composition exists between model compounds having aminederived end groups and those systems bearing acid-derived end groups. Data obtained using differential thermal analyses techniques indicate little difference in the thermal behavior of the benzimidazolones in inert or oxygen atmospheres. The changes in the amounts of carbon dioxide and carbon monoxide as a function of temperature and time support a proposal for simultaneous thermal and thermooxidation processes for the degradation of these systems in oxygen atmospheres at high temperatures.