Abstract: A lubricant composition is suitable for use in diesel engines and is resistant to degradation by oxidative by-products of biodiesel fuel. The composition includes (A) a base oil, (B) at least one diphenylamine antioxidant, and (C) at least one antioxidant. The antioxidant (C) is selected from the group consisting of a sulfur containing phenolic antioxidant, a phenyl-alpha-naphthylamine antioxidant, and combinations thereof. The lubricant composition is formed using a method. In the method, the (A) base oil has an initial oxidation value measured according to ASTM D 6186. In addition in the method, the lubricant composition includes up to about 6 wt % of the biodiesel fuel and has a final oxidation value measured according to ASTM D 6186 that is equal to or greater than the initial oxidation value of the (A) base oil.