Flex-Fuel vehicles, launched in the Brazilian market in 2003, operate with gasoline blended with anhydrous ethanol (18-25% vol/vol), 100% hydrous ethanol (4.0-4.9% vol/vol of water) or any blend of these fuels. Dynamometer tests were conducted on a 1.4 L, Flex-Fuel Otto engine. Gasoline with 25% vol/vol of anhydrous ethanol was blended with different ratios of hydrous ethanol. A programmable engine control unit was used to manage engine operation and spark timing calibration for maximum break torque at different speeds and torques. Combustion characteristics, such as mass fraction burned, heat release rate and combustion duration were calculated based on in-cylinder pressure curve data, measured by a special data acquisition system. Emissions of THC, NOX, CO, CO2, unburned ethanol and aldehydes were measured by a Fourier transform infrared analyzer. Hydrous ethanol addition reduced CO and THC, but increased CO2, aldehydes and unburned ethanol emissions. NOX results presented complex trends with ethanol addition, depending on the operating condition, spark advance timing and other parameters. (C) 2012 Elsevier Ltd. All rights reserved.