Metal surfaces have been investigated after lubrication tests with oils containing solid lubricants. With an MoS2-containing engine oil, an MoS2-film was formed on engine parts. Solids without a layer structure also formed solid films on metal surfaces at the area of frictional contact. These films are, however, not the original compounds, but products of chemical reaction.Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Montreal, Canada, October 8–10, 1974