The General Motors Corporation supplied four low emission prototype vehicles for evaluation. The test vehicles were desired to demonstrate possible 1975-76 emission control systems and to compare emissions measured by the 1972 and 1975 Federal Emission Test Procedures. The four vehicles are descirbed as follows: (1) An Oldsmobile 88 equipped with a 455 CID engine, automatic transmission, exhaust gas recirculation, an oxidizing catalytic reactor and an air pump; (2) An Oldsmobile 88 with a 455 CID engine and automatic transmission equipped with exhaust gas recirculation, dual bed oxidizing-reducing catalytic reactor and an air pump; (3) A 455 CID Oldsmobile 88 equipped with an automatic transmission, exhaust gas recirculation, two oxidizing catalysts, an air valve, and converted to run of LPG fuel; (4) A Buick Gran Sport with 455 CID engine and automatic transmission equipped with a modified intake manifold, exhaust gas recirculation, oxidizing catalyst and air pump systems. All testing was performed in accordance with the July 2, 1971, Federal Register. Tabulated results indicate while three of the vehicles tested demonstrated emission levels approaching those required for 1975 with one of these achieving 1976 levels in one test.