The recently amended U.S. Corporate Average Fuel Economy (CAFE) standards determine fuel-economy targets based on the footprint (wheelbase by track width) of vehicles such that larger vehicles have lower fuel-economy targets. This paper considers whether these standards create an incentive for firms to increase vehicle size by presenting an oligopolistic-equilibrium model in which automotive firms can modify vehicle dimensions, implement fuel-saving technology features, and trade off acceleration performance and fuel economy. Wide ranges of scenarios for consumer preferences are considered. Results suggest that the footprint-based CAFE standards create an incentive to increase vehicle size except when consumer preference for vehicle size is near its lower bound and preference for acceleration is near its upper bound. In all other simulations, the sales-weighted average vehicle size increases by 2-32%, undermining gains in fuel economy by 1-4 mpg (0.6-1.7 km/L). Carbon-dioxide emissions from these vehicles are 5-15% higher as a result (4.69 x 10(11) -5.17 x 10(11) kg for one year of produced vehicles compared to 4.47 x 10(11) kg with no size changes), which is equivalent to adding 3-10 coal-fired power plants to the electricity grid each year. Furthermore, results suggest that the incentive is larger for light trucks than for passenger cars, which could increase traffic safety risks. (C) 2011 Elsevier Ltd. All rights reserved.