Deterioration in fuel quality upon storage has been a continuing problem in the utilization of middle distillate fuels. For diesel fuels. Instability is usually defined by the formation of insoluble sediments and gums and by the accumulation of hydroperoxides. Gravimetric accelerated storage stability tests conducted with model compounds as dopants in otherwise stable distillate fuels have demonstrated that oxidative condensation reactions of polar heterocylces are deleterious to stability. In particular, nitrogen containing aromatics (pyrroles, pyridinea, indoles, etc.) appear to be very harmful. Correlation of model dopant studies with results obtained with actual unstable fuels has indicated that autoxidation processes are usually not isolated reactions but are sensitive to the presence of other fuel constituents. In an effort to learn more about potential interactive effects, we have examined the autoxidation of two model compounds, 2, 5-dimethylpyrrole and 3-methylindole, in a shale diesel fuel in the presence of a second model dopant (a hydroperoxide, organic acid or base). The results presented support the notion that such interactive effects may be of critical importance in defining the stability of actual middle distillate fuels.