The oxidation kinetics of menhaden oil containing 0% to 0.02% tertbutylhydroquinone (TBHQ) were evaluated at 37°C. Induction periods, and monomolecular and bimolecular oxidation rates were determined from thiobarbituric acid analysis. The disappearance rates of several fatty acids were determined from GC analysis. Free fatty acid and viscosity changes were evaluated. Induction periods were directly related to TBHQ concentration. Monomolecular rates decreased with increasing TBHQ concentration, but bimolecular rates did not change. The rate of disappearance of unsaturated fatty acids was proportional to their degree of unsaturation, but not related to TBHQ concentration. Free fatty acid content and viscosity increased rapidly after the monomolecular period.