The U.S. transportation sector relies almost exclusively on oil; as a result, it causes about a third of the nation's greenhouse gas emissions. Advanced technology vehicles powered by alternative fuels, such as electricity and ethanol, are one way to reduce oil consumption. The fed. gov¿t. set a goal for fed. agencies to use plug-in hybrid electric vehicles -- vehicles that run on both gasoline and batteries charged by connecting a plug into an electric power source -- as they become available at a reasonable cost. This report examined the: (1) potential benefits of plug-ins; (2) factors affecting the availability of plug-ins; and (3) challenges to incorporating plug-ins into the fed. fleet. Illustrations.