We review alternatives that have been proposed to mitigate greenhouse gas (GHG) emissions from vehicles by comparing alternatives for displacing the current suite of transportation fuels to more GHG-sparing fuels and, to a lesser extent, powertrains. Two topical approaches, biofuels and electrofuels, appear to be less effective than direct electrification of the fleet. By biofuel, we mean a fuel derived from sustainably sourced biomass or waste carbon streams. By electrofuel, we mean a fuel derived from a carbon source in which most of the stored energy stems from an electrochemical conversion. For any direct electrification (e.g., battery-powered vehicle) or indirect electrification (e.g., electrofuel) technology to significantly reduce the overall emissions of carbon dioxide and criteria pollutants from the transportation sector, the grid would need to be modernized and decarbonized.