A joint automotive and petroleum research program to develop prototype fuel and hardware requirements for low-emission vehicle systems is described. The relevance of the very stringent emission targets established by the Inter-Industry Emission Control (IIEC) program on the overall improvement in ambient air quality for the Los Angeles basin is illustrated.Three separate low-emission concept vehicle systems targeted to meet the very stringent emission targets of the IIEC program are described. Emission performance of these three systems on the recently published, more severe federal exhaust emission test procedures (July 15-November 10, 1970) are given. In addition, preliminary emission data are presented from a fourth low-emission concept vehicle system which combines the emission hardware features of the three earlier systems (thermal reactors with catalysts and an exhaust gas recirculation system).Vehicle fuel economy penalties and operating temperature problems of the low-emission concept vehicles are discussed. The limited durability experience to date has defined major problems on critical subsystem components used in these low-emission concept vehicles.A projection is made on how the emission levels achieved in these “single vehicle” research-oriented tests would increase to account for the depreciation of the emission control system with mileage and for the tolerances and variability existing in mass production.