Exergetic analysis consists in the evaluation of the exergetic balance on experimental data. When applied to an internal combustion engine, exergetic analysis can identify sources of inefficiency and potentialities for utilizing exergy that would be rejected. To perform this analysis, experimental data were acquired for different operating conditions of a spark-ignition engine by using gasohol and hydrous ethanol as fuels. With these data, an exergetic analysis was carried out by evaluating the effects of engine operating parameters on associated irreversibilities. Afterwards, a comparison between the exergetic analyses of hydrous ethanol and gasohol was presented. Finally, first and second law efficiencies were evaluated as functions of engine speed, engine load and air-fuel ratio. Exergy distributions of hydrous ethanol at different conditions and the accounts of exergy losses during engine operations were also evaluated.