Lubricating oil compositions for two-cycle (two-stroke) engines are described, of three types, comprising by weight (viscosity being kinetic at 100 DEG C) : 1. (a) 30 to 70% of a polyol ester having a viscosity of 9 to 15 cSt, (b) 30 to 70% of a diester having a viscosity of 2 to 5 cSt, (c) 1 to 5% of a polybutene having a molecular weight of 500 to 2,500 and/or 1 to 5% of a polymethacrylate having a molecular weight of 5,000 to 40,000, and (d) 5 to 25% of a dispersant. 2. (a) 30 to 70% of a polyol ester having a viscosity of 4 to 15 cSt, (b) 0 to 35% of a complex ester having a viscosity of 10 to 14 cSt, (c) 10 to 70% of a diester having a viscosity of 2 to 5 cSt, and (d) 5 to 25% of a dispersant. The dispersant (d) is preferably a polyamide; it prevents formation of deposits on the engine. 3. A lubricating base oil contains 5 to 25% of a polyamide type of dispersant and also a neutral calcium sulfonate and a neutral calcium salicylate which together amount to 0.1 to 5% by weight of the composition. The base oil can be a mixture of components (a) to (c) of composition 1 or 2, a mineral oil or a poly- alpha -olefin. The compositions can have other additives, and can be used as a low-oil, e.g. 100:1, mixture with gasoline, and they have good biodegradibility.