Low temperature air oxidation affects many aspects of the fuels buses: weathering, storage stability, hardening, and fouling. Addition reactions taking place during the autoxidation of different heterocydic compound classes were studied at 130 degrees C. This investigation reports on the conversion, product selectivity, nature of addition products, and plausible mechanisms that would explain the observations subsequent to the oxidation of indole, 2,3-dihydroindole, quinoline, benzofuran, 2,3-dihydrobenzofuran, and thianaphthene. Of these, indole is known to be prone to oxidative addition; Among the five-membered heterocyclic compounds, the propensity to form oxidative addition products increased in the order: S << O < N. Addition took place mainly through C-C bond formation. In comparison to hydrocarbons, it was surprising to find that indole and 2,3-dihydroindole were less prone to oxidative addition than the five-membered naphtheno-aromatic hydrocarbon analogues indene and indan. On the basis of the work, some implications for low temperature oxidation processes, and free radical processes in general, are discussed.