The shale gas revolution in the United States has reduced the price of natural gas (NG) significantly. Combined with new fuel and vehicle technologies, an opportunity exists to expand the use of NG throughout the economy, including in the light-duty fleet of cars and trucks. This expansion could involve the direct combustion of the gas in the form of compressed natural gas or liquid petroleum gas or, alternatively, the use of natural-gas-based liquid fuels such as ethanol or methanol. This paper examines the potential economic, environmental, and national security gains from replacing a portion of the domestic gasoline use in the light-duty fleet with these various NG-based fuels. Also examined are the regulatory barriers to the expanded use of the fuels. We find that certain NG-based fuels could yield significant fuel cost savings relative to conventional gasoline in the light-duty fleet, along with gains to national security and, possibly, some environmental benefits.