A series of bench engine tests and field trials have been carried out using Japanese domestic engines and vehicles. Various motor oil viscosity grades were evaluated in order to select the best for fuel savings. A laboratory evaluation to assess friction behavior and antiwear properties was used to select suitable friction modifiers for formulating fuel saving motor oils. In general, higher oil consumption was obtained with lower viscosity oils. In some cases piston and bearing seizure occurred under severe operating conditions. Valve train wear performance of the lubricant appeared to depend mainly on the additive type used.From these experimental studies, it was determined that a viscosity grade of “7.5W-30” was best for fuel efficiency, engine performance and durability in current Japanese vehicles.Fuel efficiency was further improved by incorporating an organic Molybdenum compound as a friction modifier in the formulation.