Oxygen and moisture are shown to cause a significant increase in friction and wear under non-scuffing conditions. In certain cases, wear in humid air is destructive, but can be entirely eliminated by blanketing the system in dry nitrogen. This pro-wear effect of air is entirely reversible it occurs with most metallurgies and lubricant types, and it may be controlled by incorporating suitable additives in the oil. Various wear mechanisms have been examined to explain the experimental results; the most satisfactory is a simple corrosive wear phenomenon, involving the formation and rubbing away of metal oxides.Presented at the ASME/ASLE Lubrication Conference, Atlantic City, New Jersey, October 8–10, 1968.