Despite the fact that the major component of any lubricant package is the base oil, its reaction with the environment and substrate and the effect on the frictional behavior of the contact are not well understood. The present work was accomplished in a custom ultrahigh vacuum chamber that permits measurement of the friction coefficient during a ball‐on‐disk test and insitu Auger electron spectroscopy (AES) of disk surfaces tested under vacuum conditions. Results for 52100 steel lubricated with poly‐α‐olefin (synthetic base oil) show a more rapid decrease in contact life (distance slid to failure) with increasing load in vacuum than in air. Vacuum tests at an average Hertzian pressure of 550 MPa exhibited essentially zero life while tests in air at the same load survived 10 km of sliding. Preliminary AES results indicate that maintenance of a thick oxide is connected with extended contact life.

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