A spark ignition engine was used to determine the influence of fuel composition on the exhaust emissions of regulated pollutants and specific hydrocarbons. Two specific fuel matrixes were used: the first contains eight hydrocarbons and the second also four oxygenated compounds. Fuel aromatics increased the exhaust CO, hydrocarbon (HC), and NO x. The addition of oxygenated compounds could decrease exhaust CO, HC, and NO x up to 30, 50, and 60%, respectively. Under these conditions, the addition of 5% of 2-propanol was the most effective for the reduction of CO. The addition of 20% of ethanol for the reduction of HC and this of 5% of MTBE for the NO x. The influence of fuel composition on the emission of gt; 20 individual hydrocarbons was also presented. The emissions of all HC generally decreased with the addition of oxygenated compounds, except sometimes in the case of methane, ethane, ethylene, propylene, isobutene, and cyclohexane, which increased. The percentages of these HC in the exhaust gas of the commercial fuel were calculated. Several models correlating the exhaust concentration of these pollutants with the fuel composition were also presented. This is an abstract of a paper presented at the 7th World Congress of Chemical Engineering (Glasgow, Scotland 7/10-14/2005).