Changes in the liquid-phase oxidation of a cycloparaffinic/paraffinic solvent resulting from the introduction of natural and synthetic fuel antioxidants are studied by tracking the depletion of dissolved O-2 in a closed system at 185 degrees C and 3.2 MPa. A Jet-A fuel of reduced thermal stability is the source of natural fuel antioxidants that are introduced by making dilute (<20%) blends with the solvent. The synthetic hindered-phenol antioxidant BHT is added at concentrations of 3-50 mg/L. The individual and combined effects of natural and synthetic antioxidants on paraffin autoxidation are determined on the basis of increased reaction time required to deplete initial dissolved O-2 by 50%. Synergistic effects of similar to 40% are observed for certain antioxidant concentrations. The roles of natural and synthetic antioxidants in the liquid-phase oxidation of jet fuel are discussed.