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Abstract: The increasing number of automotive vehicles around the world is responsible for the emission of great amounts of pollutant gases, which can cause serious problems to environment and to human health. Among the fuels used in light vehicles, two of them deserve special mention: gasoline, hegemonic fuel in the world scenario and ethanol, whose consumption is rapidly increasing, once it is a renewable fuel that mitigates emissions of carbon dioxide. The Brazilian ethanol program is now supported by 2 basic factors: the mandatory use of ethanol blend in gasoline, and the expanding market for flex-fuel cars. The gasoline sold in Brazil has 20% to 25% of anhydrous ethanol, and approximately 90% of the new cars sold use flex fuel engines. Therefore, it is necessary to develop methodologies to assess the emissions from gasoline and ethanol engines. In this work, an Electrochemical Analyzer was employed to detect important pollutant gases, as carbon monoxide (CO), nitrogen oxides (NOx), and sulfur dioxide (SO2) from the exhaust of gasoline and ethanol (including flex-fuel) powered vehicles. These gases can cause serious damages to human health, besides causing environmental problems, as acid rain. Furthermore, CO and NOx are primary pollutants in the formation of the tropospheric ozone, which is an important greenhouse gas and causes the photochemical smog. Finally, based on data experimentally obtained, we could perform a comparative analysis of the pollutants emission from gasoline and ethanol powered vehicles. We could notice that gasoline powered vehicles had greater NOx emission than ethanol powered vehicles, as it was expected. Nevertheless, this difference could not be observed in CO and SO2 emission, once both ethanol and gasoline powered vehicles emitted considerable amount of CO and SO2 in the range of ppmV. We could also notice that pollutant emissions are strongly related to many factors, such as the vehicle manufacture date, model, engine rotation speed and vehicle maintenance. [Copyright &y& Elsevier]