Vehicle durability data using the Gould NOx catalyst system is presented. Two 1973 vehicles accumulated 25, 000 AMA miles each demonstrating efficient and stable control of NOx, HC, and CO vehicle exhaust emissions.In additional tests, accurate fuel economy data using a 1975 California vehicle were taken. The vehicle system was optimized such that the fuel economy was improved by 2. 6% while meeting the 1978 emission standards of 3. 4 gram per mile CO, 0. 41 gram per mile HC, and 0. 4 gram per mile NOx.