The mechanism of autoxidation reaction fouling in single phase liquid heat transfer under turbulent flow conditions was studied using model solutions of indene in lube oil recirculated through a tubular fouling probe which permitted both thermal and mass deposition measurements. The fouling rate was initially constant, and then accelerated as polyperoxide gums reached their solubility limit. Deposit composition and morphology in the tubular device are compared with results obtained in an annular probe with a short heated length. The initial fouling data collected over surface temperatures of 180-255 degrees C and now velocities of 0.5-2.6 m/s (Re = 3000 - 16000) gave reasonable agreement with a boundary layer reaction model.