The mechanism of boundary lubrication of organic disulfides in while oil, using four-ball test data, has been studied by examining the influence of load, wear test time, concentration and structure. The amounts of iron sulfide, thiol and elemental sulfur fanned from disulfides have been quantitatively determined in oil solution and wear debris. Monosulfide was identified in oil solution after wear test. Temperature in wear junction and additive concentration in oil control the rate and magnitude of sulfur products formation. The formation of iron sulfide occurs by decomposition of disulfide to elemental sulfur and thiol, which than read with the metal surface giving sulfide. The separate chemical reaction paths of disulfides with different rates and amounts of sulfur products formation depended on the lubrication conditions present. The chemical structure of disulfides influences the formation of determined sulfur compounds.Presented at the 42nd Annual Meeting in Anaheim, California May 11–14, 1987