Boundary lubrication by hydrocarbons was explored by using a four-ball machine with 52100 steel specimens at 0.35 cm per second sliding velocity. The chemical type of the hydrocarbon and the amount of oxygen dissolved in it appeared important. Low molecular weight liquid aromatic hydrocarbons exposed to ambient air were found as effective as straight mineral oils in controlling wear, while saturated hydrocarbons usually were markedly poorer. Benzene and cyclohexane were used as model lubricants in the study of oxygen concentration in vapor and liquid phase. Both high and low oxygen-to-hydrocarbon ratios favored high wear and inorganic wear products. Certain intermediate ratios favored low wear and the formation of an oxygenated organic “friction polymer” which prevented metallic contact. Results are discussed in the light of knowledge concerning catalytic reactions at clean metal surfaces.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Washington, D.C., October 13–16, 1964.