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 4.5 or less, and (B) an overbased metal hydrocarbyl-substituted hydroxybenzoate detergent having a basicity index of greater than 4.5. The ratio of detergent (A) to detergent (B), both expressed as mass of active ingredient, is in the range from 0.5 to 15. The trunk piston marine engine lubricating oil composition has a TBN (using ASTM D2896) of 20 to 60.