This paper presents new techniques for the interpretation of engine and vehicle results on prototype fuel-efficient motor oils. A case history is presented which follows the component selection process through laboratory friction and bench engine screening tests. The resulting optimized lubricant formulation was demonstrated in an automobile dynamometer test, resulting in approximately 2% better MPG than that of the proposed ASTM SAE 20W/30 reference oil.The capabilities and limitations of the available test methods are discussed from the perspective of PARAMINS experience. An important part of FE data interpretation is the comparison of experimental results to the estimated maximum realizable friction reduction and fuel savings potential. This requires an understanding of the portion of total mechanical friction contributed by solid-solid (boundary) friction and by viscous (hydrodynamic) losses. The authors show how laboratory friction measurements were used as a means for examining vehicle results in these terms.