1. Contact angles of lubricating oils on St. 45 steel have been determined at elevated temperatures (up to 180°C), and it has been shown that increasing the temperature leads to a decrease in the contact angle at a rate that is fast at first and then slower. At 180°C, contact angles for the different oils are quite similar. 2. The presence of oxidized films on a metal sharply decreases the contact angle for all of the oils that were investigated. 3. The oxidation of a hydrocarbon oil on a metal will form a film that gives a considerable increase in the contact angle of the original oil. 4. Possibilities have been pointed out for the practical utilization of wettability reduction, by depositing films of oil oxidation products on metal surfaces.