The paper summarizes research on the use of intermediate ethanol blends in the U. S. vehicle fleet. Intermediate ethanol blends, fuels with ethanol content above 10%, are just being introduced in the U. S. for use in conventional vehicles. Thirty published studies are covered including the extensive program conducted by the Coordinating Research Council. The individual studies are grouped by vehicle performance aspect: driveability, exhaust emissions, evaporative emissions, flexible-fuel vehicles, onboard diagnostics, and durability of engine, fuel, and emissions control systems. Within each performance aspect, data are examined for common trends and potential fuel impacts. In some cases, results from similar programs are combined and analyzed. A variety of ethanol impacts on vehicle performance and emissions are identified and described. Emphasis is placed on impact areas or potential failure modes that have been identified and tested. Differences in vehicle responses to increasing ethanol content are identified. Some of the studies concluded that intermediate ethanol blends have similar performance to gasoline or low level ethanol blends in a number of areas including short-term driveability and emissions and exhaust catalyst and evaporative control system durability in the post-2001 vehicles tested. However, there are areas where research has identified potential adverse impacts from intermediate ethanol blends including false illumination of Malfunction Indicator Lights and reduced engine and fuel system durability.