A wide range of air/fuel ratios and exhaust gas recycle rates were examined in an automotive test engine for the purpose of reducing NOx emissions to low levels. A minimum NOx level of 0.4 g/mile on the 1972 Federal Test Procedure was obtained at a rich A/F of 12 and a recycle rate of 25%. With this combination, the fuel consumption increased approximately 15% and the wide open throttle (WOT) power decreased about 30%. Combustion in the cylinders was good and the vehicle operated smoothly. Comparable results were not obtained with lean mixtures. The results of this study do not establish the feasibility of meeting the 1976 NOx standard with the rich mixture, high recycle technique. Further, the increased CO and HC emissions would have to be controlled by exhaust gas treatment.