Improvements in motor oil fuel efficiency have been mainly achieved through lower viscosity and usage of friction modifiers. Further reduction in viscosity to below SAE #20 could be useful for improvement of fuel efficiency. JASO gasoline engine tests were conducted with an ultra low viscosity oil containing mineral base stocks that showed minimum drive torque during an engine motoring test. The results showed an increase in viscosity, increase in oil consumption and deterioration of detergency. In order to solve these problems, an ultra low viscosity engine oil formulated by a special synthetic base stock with improved volatility was developed. The results of a High Temperature Oxidation Test showed this synthetic oil to have better performance than the mineral oil.