The oil immersion test is a useful method to investigate the interaction between steel bearings 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 with various weight ratios in liquid paraffin were conducted at a temperature of 180 degrees C for a test time of 60 min under a N-2 atmosphere. The relative thicknesses of the films formed were examined using Auger electron spectroscopy (AES). The friction coefficient and wear life of the film formed in oil immersion tests were evaluated using a one-way reciprocating friction tester under dry friction conditions against a steel ball at room temperature, and the results were compared with the wear results of films formed under an air atmosphere. AES analyses indicate that under N-2 atmosphere, a thicker chemical reacted surface film on the steel block was formed as compared with the film formed at the same immersion test conditions but under an air atmosphere. Friction and wear tests show that films formed under a N-2 atmosphere exhibit a longer wear life than that of the films formed under air atmosphere. This investigation demonstrates that the film thickness is affected by the weight ratio of SO to DBP, while the antiwear behaviour of the film formed in an S/P weight ratio of 80 oil seems to be the best in terms of the wear life per unit thickness of the film.