Applying lubricants is one of the most important measures to reduce friction and wear. Improving the mechanical efficiency of engines and gears by reducing the frictional losses in the mixed film and in the fluid film lubrication regime in principle facilitates the reduction of fuel consumption of the engine or of the energy needed to operate the cars.The maximum consumption reduction that is theoretically possible with lubricating measures is estimated by means of the efficiency analysis of engines and gears and the proportionate effects of lower viscosity and additives reducing friction are evaluated. The estimate is made on the basis of the given relationship between friction and fuel consumption. Obviously, the possible consumption reductions at partial loads and lower temperatures are higher than at full load and operating temperature. This determines the relevant consequences regarding the possible total energy reductions under political economy aspects. It will be shown that these states of operation, resulting in the highest reductions of fuel, only cover a relatively small range of the total operating times of vehicles. Therefore possible reductions are more limited than normally is assumed when particulary unfavorable conditions are taken as a basis for estimating the effects of lubricant-based measures. The results of this analysis leading to a realistic assessment of total reductions are compared with published data, which will be critically evaluated.