This paper develops analytical models to estimate the welfare effects of higher Corporate Average Fuel Economy (CAFE) standards on new passenger vehicles. The analysis incorporates a broad range of fuel-and-driving-related externalities, fuel taxes, different assumptions concerning consumers' valuation of fuel saving technologies and their alternative value in enhancing other vehicle attributes, and endogenous vehicle fleet composition. To implement the analysis, we develop estimates of CAFE's impact on local pollution, nationwide congestion, and traffic accidents. We find that higher fuel economy standards can produce anything from moderate welfare gains, to very little or no effect, to substantial welfare losses, depending on how consumers value fuel economy technologies and their opportunity costs.