The mechanism of autoxidation reaction fouling was studied using model solutions of an active alkene, indene, in two inert solvents. Fouling was caused by the formation of insoluble polyperoxide gums and was controlled by the bulk chemical reaction in the recirculating system. Once the gums adhered to the surface they aged to form complex, oxygenated solids. The deposition mechanism was determined by the solubility of the polyperoxides in the solvent; an initial, linear fouling rate associated with the reaction of soluble gums in the thermal boundary layer was followed by an accelerating rate as insoluble agglomerates were deposited once the solubility limit of the polyperoxides was reached. The chemical mechanism was studied in separate batch reactions and significant solvent nature effects were found.