A trunk piston marine engine lubricating oil composition for a medium-speed compression-ignited marine engine comprises, in a major amount, an oil of lubricating viscosity containing 50 mass % or more of a Group II basestock, and, in respective minor amounts, (A) an overbased metal hydrocarbyl-substituted hydroxybenzoate detergent having a basicity index of 5.5 or greater, and (B) an overbased metal hydrocarbyl-substituted hydroxybenzoate detergent having a basicity index in the range of 2.1 to 5.4. The ratio of the mass of metal in detergent (A) to the mass of metal in detergent (B) is 1 or less. The trunk piston marine engine lubricating oil composition has a TBN (using ASTM D2896) of 20 to 60.