Automotive engine output and efficiency have greatly improved over the years due to the combined efforts of the automotive and petroleum industries. As compression ratios and octane ratings of fuels have increased, the automotive engineer has been able to give the customer more for his money in either economy or performance, or a combination of both.A brief history of these developments should serve to point to the problems of the future, since octane requirements of the 1971 models have been generally reduced to enable the automobile manufacturer to meet the stringent exhaust emission standards.Since lead antiknocks are the most economical and widely used method of increasing the octane rating of gasoline, their effects on engine parameters such as durability, ORI, and emissions will be compared with lead-free gasolines.The economic impact of the change from the 94 and 100 octane number fuels to a 91 octane lead-free gasoline will be presented. Consideration will be given to the question of how much control from automobiles is really needed to achieve a satisfactory level of ambient air quality.The future of the piston engine, as well as possible substitutes, is discussed in view of the stringent emission controls proposed for 1975 and 1976. A critical review of both the ambient air quality and emission standards indicates the need for revisions and a careful evaluation of the cost-benefit ratio, so that the passenger car buyer will not be needlessly penalized with both high initial costs and high operating costs. The potential waste of our national resources must also receive consideration.