The oil immersion test is a useful method to investigate the interaction between steel-bearing and oil additives. In this work, oil immersion tests of steel blocks with sulfurized olefin (SO), dibutyl phosphite (DBP), and the combination of SO and DBP in various weight ratios in liquid paraffin were conducted at a temperature of 180 degrees C for a test duration of 60 min. The chemical composition of the film formed was examined using both X-ray photoelectron spectroscopy and Auger electron spectroscopy. The friction coefficient and wear life of the films formed in the oil immersion tests were evaluated using a one-way reciprocating friction tester under dry friction conditions against a steel ball at room temperature. The performance of the liquid paraffin containing SO, DBP or the combination of SO and DBP was also investigated with a four-ball wear tester. Results indicate that with the S/P weight ratio at 55, a lower friction coefficient and longer wear life of the film formed in the immersion test can be observed. Test results demonstrate that the wear life of the film formed in the oil immersion tests are in good agreement with the wear results of the conventional four-ball wear test.