The significantly higher oxidation stability obtained on deuteration of the acid moiety of a neopentyl polyol ester is the result of two effects, viz, the deuteration effect and the synergistic effect of alkali metal compounds with the antioxidant. The enhancement in oxidation stability attributable to 96 atom percent deuteration appears to be three-to-fourfold at 220°C. The enhancement due to the alkali metal effect appears to be about thirtyfold. Preliminary results indicate that at higher deuterium concentration levels (>96 atom percent), the oxidative stability of the ester, deuterated on the acid moiety, is further increased.Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Hartford, Connecticut, October 18–20, 1983