A gear oil composition is provided having fuel saving performance and providing gears or bearings with sufficient durability. The composition includes a base oil having a blend of (A) a mineral lubricating base oil having a 100° C. kinematic viscosity of 2 to 6 mm2/s, a % CA of 0.5 or less and a tertiary carbon content of 7% or more and (B) a solvent-refined mineral lubricating oil having a 100° C. kinematic viscosity of 10 to 70 mm2/s in an amount of 2 to 40 percent by mass based on the total base oil composition mass; (D) zinc dialkyldithiophosphate in an amount of 0.02 to 0.5 percent by mass based on the zinc amount; and (E) an alkaline earth metal detergent having a base number of 100 mgKOH/g or greater in an amount of 0.1 to 0.5 percent by mass, based on the metal amount, of the gear oil composition mass.