This paper describes sulfate emission data that were gathered on a series of 2.3L and 400 CID engine vehicles during a test program conducted from April, 1975, to September, 1975. The sulfate data were obtained from production vehicles, with and without catalysts, as well as prototype vehicles equipped with various advanced concept emission control systems such as lean reactor and pre-chamber engines, electronic fuel injection, and three way catalysts. Monolithic and pelleted catalysts, aged 4,000 miles, were tested, with and without thermactor air. A monolithic catalyst, aged 50,000 miles, also was evaluated.Determinations were made of the variability of the sulfate emission data from various test cycles and the effect of catalyst pre-conditioning temperature on initial sulfate test levels was studied. An effect due to the size of the vehicle cooling fan during chassis roll testing also was noted.The 1974 production (non-catalyst) and lean burn prototype (non-catalyst) vehicles convert ≤2% of consumed fuel sulfur to sulfates and are essentially equivalent in this regard.Vehicles with catalysts convert from 1 to 60% of fuel sulfur to sulfates depending upon temperature, oxygen in the exhaust gas, prior catalyst history and test cycles.