COST PER YEAR is calculated assuming 15,000 miles driven (55 percent on highways, 45 percent in city) from fuel prices current as of March 20, 2013, except biodiesel (September 12, 2007) and hydrogen (September 12, 2007).
EMISSIONS encompass carbon dioxide produced by fuel processing ("production") and car operation ("tailpipe"). Ethanol (E85) has a negative "production" value because corn absorbs more CO2 from the atmosphere than it emits during harvesting and fuel processing.
Data sources: Argonne National Laboratory GREET v1.7 (emissions data), Dept. of Energy Alternative Fuels Data Center (number of available models, number of fueling stations, gasoline-gallon equivalents), Dept. of Energy Clean Cities Alternative Fuel Price Report (cost data), Dept. of Energy Energy Information Administration (size of U.S. fleet), National Hydrogen Association, National Biodiesel Board.