Reducing viscosity of automotive gear oil is expected to save fuel consumption. However, it contributes to lowering oil film thickness and causes deterioration of fatigue strength. The fatigue strength of several automotive gear oils is studied, as well as the influence of viscosity and formulation of these oils. The test gear oil was injected into the rolling contact surface under the condition of oil temperature at 353 K. Rolling fatigue life was affected with viscosity properties of gear oil. The slope of p-N curve depended on the additives type. This is an abstract of a paper presented at the 2009 World Tribology Congress (Kyoto, Japan 9/6-11/2009).