Records for 20,728 passenger cars covering 1967 through 1977 models were analyzed to see the effects of emissions controls on fuel economy. Data on weight, engine displacement, compression ratio, carburetion, transmission type, axle ratio, air conditioning, and miles driven per month were obtained for each car. Linear regression analyses of these data showed design changes during this period affected fuel economy significantly. Around 1973, there were appreciable decreases in fuel economy relative to 1967 models, whereas for 1975 through 1977 increases were observed. Fuel economy for cars meeting California emission standards was lower than for those meeting Federal standards.