An additive composition prepared by reacting a polymer prepared from ethylene and at least one C.sub.3 -C.sub.10 alpha-monoolefin and optionally a polyene selected from non-conjugated dienes and trienes comprising from about 15 to 80 mole percent of ethylene from about 20 to 85 mole percent of said C.sub.3 -C.sub.10 alpha-monoolefin and from about 0 to 15 mole percent of said polyene and having an average molecular weight ranging from about 5,000 to 500,000 with a nitrosodiphenylamine compound represented by the formula: ##STR1## in which R and R.sup.1 represent hydrogen or an alkyl, alkenyl, or alkoxyl radical having from 1 to 8 carbon atoms, and a lubricating oil composition containing same is provided.