A spark ignition engine was used to study the impact of fuel composition and of the air/fuel equivalence ratio on exhaust emissions of specific hydrocarbons. The fuel blends used contained eight main hydrocarbons and four oxygenated compounds. The identification of each exhaust pollutant fuel precursor is already done. After this identification, several models correlating the exhaust concentration of these pollutants with the fuel composition are presented on each air/fuel equivalence ratio. Based on the above findings, the main formation paths for the formation of each exhaust pollutant are proposed. (C) 2004 Elsevier Ltd. All rights reserved.