A lubricating oil additive composition which imparts improved oxidation properties to crankcase lubricants comprises an antioxidant selected from aromatic or alkyl sulfides and polysulfides, sulfurized olefins, sulfurized carboxylic acid esters and sulfurized ester-olefins, and a tertiary amine of the formula (R).sub.3 N wherein each R is independently C.sub.3 -C.sub.10 alkyl, phenyl or phenyl substituted by 1 or 2 alkyl groups of up to 12 carbon atoms. Lubricating oil compositions containing this additive composition are also disclosed.