An internal-combustion engine lubricating oil composition has a P content of not greater than 0.09 mass %; a S content of not greater than 0.3 mass %; and a sulphated ash content of not greater than 1 mass %. It contains the following additives: as sole ashless, nitrogen-containing dispersant, and providing from 0.03 to 0.07 mass % of nitrogen in the lubricating oil composition, at least one ashless, nitrogen-containing derivative of a polyalkenyl-substituted mono- or dicarboxylic acid, anhydride or ester, the polyalkenyl-substituted mono- or dicarboxylic acid, anhydride or ester being made from a polyalkene exclusively by the thermal “ene” reaction; as sole overbased metal detergent, at least one overbased alkaline earth metal sulfonate; and at least one viscosity modifier.