This paper covers work performed for the California Air Resources Board and US Environmental Protection Agency by Southwest Research Institute. Emission measurements were made on four in-use off-road two-stroke motorcycles and all-terrain vehicles utilizing oxygenated and non-oxygenated fuels. Emission data was produced to augment ARB and EPA's off-road emission inventory. It was intended that this program provide ARB and EPA with emission test results they require for atmospheric modeling.The paper describes the equipment and engines tested, test procedures, emissions sampling methodologies, and emissions analytical techniques. Fuels used in the study are described, along with the emissions characterization results. The fuel effects on exhaust emissions and operation due to ethanol content and fuel components is compared.The emission changes observed when fuel was switched between 0% and10 % ethanol were a reduction in total hydrocarbon and non-methane hydrocarbon emissions by 3 to 24%, carbon monoxide emissions were reduced by 3 to 26%, and particulate matter emissions were reduced by 4 to 29%. Conversely, oxides of nitrogen emissions increased by 14 to 58%, and aldehyde emissions increased with oxygenated fuels. Fuel economy tended to decrease with the use of 10% ethanol fuels.