Internal combustion engines exhibit improved efficiency of the emissions control system by using a lubricating oil composition of a base oil, an alkali or alkaline earth metal-containing detergent; a metal salt of one or more phosphorus-containing compounds represented by the formula (I), wherein X.sup.1 and X.sup.2 are independently O or S, and R.sup.1 and R.sup.2 are independently hydrocarbyl groups, the average total number of carbon atoms in R.sup.1 and R.sup.2 for the one or more phosphorus-containing compounds being at least 10.4; and an acylated nitrogen-containing compound having at least about 10 alphatic carbon atoms and a TBN of at least about 2; the lubricating oil composition being characterized by a phosphorus concentration of up to about 0.12% by weight and the substantial absence of copper, thereby generating a lean-phosphorus containing exhaust gas.