Recent engine testing on separate neutral and basic zinc dithiophosphates (ZnDTPs) showed a difference in valve train wear performance, with the neutral ZnDTP giving statistically better wear inhibition in Sequence VE tests. Since the literature was lacking on the oxidation inhibition performance of the separate neutral and basic salts, we systematically examined the relative antioxidancy of several neutral and basic ZnDTP salts in various formulations. The results were dependent on the type of base oil and formulation used, and the presence of other additives.31P NMR Spectroscopy, coupled with Oxidator Bench Test studies, were used to reach these conclusions.Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999