The paper highlights the use of a light duty axle efficiency test for evaluating the fuel economy performance of automotive gear lubricants. Both final peak axle temperatures and torque efficiencies are recorded for several multigrade automotive gear lubricants. The dependence of temperature on torque efficiencies for the gear lubricants tested are discussed for a variety of driving conditions: city, highway and severe service. Temperature and torque efficiency data show strong dependence on additive system and viscosity- temperature characteristics of the gear lubricants under different driving conditions. A discussion of lubricant rheology and its importance to maintaining film strength for adequate bearing and gear lubrication as related to optimum torque efficiency and axle temperature under varying loads and pinion speeds is also provided.