The replacement of hydrogen atoms with deuterium atoms in a synthetic hydrocarbon lubricant has been shown to substantially improve its oxidation resistance. In addition, it was determined that the antifriction bearing performance life of a MIL-G-81322 grease, formulated with the deuterium substituted fluid, increased significantly at 400 F. The results of this investigation are presented along with an explanation based on the thermodynamic and kinetic differences between the carbon-hydrogen chemical bond and the carbon-deuterium chemical bond.Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Miami Beach, Florida, October 21–23, 1975