This paper investigates fuel consumption and pollutant emissions from a vehicle operating with gasoline-ethanol blend (E22), hydrous ethanol (E100) and hydrogen produced on-board. The study aims to find out if hydrogen can contribute to reduce fuel consumption and emissions. Hydrogen was produced by a hydrolytic cell adapted to the vehicle, and was mixed to the air charge in the intake pipe. A production automobile powered by a 1.0-L flexible fuel engine was used in the tests. The vehicle was tested on a chassis dynamometer, with the engine operating at idle speed and at 1400 rev/min. The results show that small amounts of hydrogen can provide stable engine operation with lean fuel-air mixture and, thus, reduce fuel consumption without compromising exhaust emission levels. Reductions of up to 11.8% and 13.1% on fuel consumption were obtained for E22 and E100, respectively.