The first round of emissions testing of light-duty alternative fuel vehicles placed in the U. S. federal fleet under the provisions of the Alternative Motor Fuels Act was recently completed. This undertaking included 75 Dodge B250 vans, of which 37 were dedicated compressed natural gas models, and 38 were standard gasoline controls. Data were collected on regulated exhaust emissions using the federal test procedures, and on a number of other quantities, through a statistically controlled program of investigation. Fuel economy results were also recorded. All test vehicles were operated in routine federal service activities under normal working conditions, adhering as closely as possible to Chrysler's prescribed maintenance schedules.The data analysis conducted thus far indicates that the compressed natural gas vehicles exhibit notably lower regulated exhaust emissions, on average, than their gasoline counterparts, and that these values are well within U.S. Environmental Protection Agency standards. In addition, lower levels of toxic constituents are emitted by the compressed natural gas vehicles relative to their gasoline counterparts, and they produce lower levels of ozone precursors as well-both characteristics that are highly desirable in contemporary transportation fuels. The compressed natural gas vehicles obtain slightly lower fuel economy than their gasoline counterparts on an energy equivalent basis.To promote the use of alternative fuels and development of an alternative fuel vehicle (AFV) industry, the Alternative Motor Fuels Act (AMFA) of 1988 requires the U.S. federal fleet to include as many AFVs as practicable. The Energy Policy Act (EPACT) of 1992 tightened the requirements for the federal fleet, requiring new vehicle purchases to be comprised of an increasing percentage of AFVs, up to a maximum of 75%, by 1999. The U.S. Department of Energy is responsible for tracking and reporting the performance of these vehicles on an annual basis to facilitate ongoing evaluation of AFV technology, and for assessing the viability of AFVs in commercial and private applications. Performance measures include driver acceptance, fuel economy, operational cost, cost and level of maintenance, and emissions output.The most extensive effort of its kind, the AMFA evaluation program targets three alternative fuels-methanol, ethanol, and compressed natural gas (CNG)-and encompasses several different types of vehicles, makes, and models operated in a number of federal service applications at various sites around the country. Light-duty passenger cars, vans, and trucks are included, along with school buses, transit buses, and heavy-duty trucks. The earliest AMFA vehicles have been in service since 1991.One of the objectives of the AMFA light-duty test program is to compare the emissions of AFVs in actual service to those of otherwise identical vehicles operating on conventional fuel. Detection of emissions deterioration as a result of age and use is of particular interest. In all cases, reformulated gasoline (RFG) is used as the basis of comparison in laboratory tests.This paper specifically addresses the emissions performance of light-duty federal fleet AFVs operating on CNG. The information reported here covers emissions test results from 75 Dodge RAM B250 vans, 37 of which are dedicated CNG models, with the remaining 38 being standard gasoline versions (controls). The data represents results solely from Round 1 of a three-round testing program, (hence, emissions deterioration is not specifically addressed).