PROBLEM TO BE SOLVED: To provide a gear oil compsn. which is excellent in high-temp. stability and is suitable for gears operated under severe conditions.
SOLUTION: This compsn. contains at least one ester represented by the formula (R1 is a 1-3C alkyl; and R2, R3, and R4 are each independently 4-10C alkyl), at least one poly-α-olefin having a kinematic viscosity of 4-50 cSt at 100°C, and at least one compd. selected from among succinimide and its derivs. and has a kinematic viscosity of 7-20 cSt and a flow point of -25°C or lower.