Lubricating oil composition

A lubricating oil composition comprising:

• (A) a lubricating base oil containing 3% by weight or less of aromatics, 20% by weight or more of monocyclic naphthenes, 50 ppm by weight or less of sulfur and 50 ppm by weight or less of nitrogen, having a viscosity of 2 to 50 mm.sup.2 /s at 100.degree. C.;
• (B) at least one compound selected from diarylamines of the general formula:
• ##STR11## wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4, which may be the same or different, each represent hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms, provided that at least one of them is a hydrocarbon group having 3 to 18 carbon atoms, or ##STR12## wherein R.sup.5 and R.sup.6 are hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms, in an amount of 0.05 to 3% by weight of the total weight of the composition, and
• (C) at least one oxymolybdenum compound selected from oxymolybdenum sulfide dithioxanthogenates of the general formula:
• ##STR13## wherein R.sup.11 and R.sup.12, which may be the same or different, each represent a hydrocarbon group having 1 to 30 carbon atoms, and X and Y, which may be the same or different, each represent oxygen or sulfur atom, in such an amount that the amount of molybdenum is 50 to 2000 ppm by weight of the total weight of the composition.