Vehicle fuel economy will continue to increase in importance as world vehicle production grows and fuel supplies become more limited year by year.As OEMs strive to produce cars and trucks with greater fuel efficiency and extended durability,additive technology developers are increasingly being asked to contribute to these goals from the lubricant side.Axle inefficiency can account for as much as 10% of the overall losses in an automotive driveline so improvements in axle efficiency can contribute greatly to improving vehicle fuel economy.For good durability,low axle oil operating temperatures are also needed to minimize oxidative and thermal degradation of the oil,reduce deposits and sludge formation,and extend oil drain intervals.To develop gear oils that can increase axle efficiency significantly while maintaining stable operating temperatures requires rig tests that are fast,precise and reproducible.This paper documents the development of a new axle test rig and test procedures and presents test results on several gear oils.The test results show the contributions of base oil viscosity,base oil chemistry,and additive chemistry on the fuel economy and temperature of the various oils.Having a dependable tool is enabling the development of new fuel-efficient and durable gear oil technology. Vehicle fuel economy will continue to increase in importance as world vehicle production grows and fuel supplies became more limited year by year. As OEMs strive to produce cars and trucks with greater fuel efficiency and extended durability, additive technology developers are increasingly being asked to contribute to these goals from the lubricant side. Axle inefficiency can account for as much as 10% of the overall losses in an automotive driveline so improvements in axle efficiency can contribute greatly to improving vehicle fuel economy. For good durability, low axle oil operating temperatures are also needed to minimize oxidative and thermal degradation of the oil, reduce deposits and sludge formation, and extend oil drain intervals.To develop gear oils that can increase axle efficiency significantly while maintaining stable operating occasions require rig tests that are fast, precise and reproducible.This paper documents the development of a new axle test rig and test procedures and presents test results on several gear oils. The test results show the contributions of base oil viscosity, base oil chemistry, and additive chemistry on the fuel economy and temperature of the various oils. Saving a dependable tool is enabling the development of new fuel-efficient and durable gear oil technology.