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 fuel components that produce each exhaust pollutant are identified. The emissions of all HC generally decrease with the addition of oxygenated compounds, except sometimes in the case of methane, ethane and cyclohexane. Under rich conditions, the relative increase of exhaust methane and benzene is more important than the other saturated HC. Some HC are correlated with the physical properties of the fuel and other exhaust pollutants. (C) 2004 Elsevier Ltd. All rights reserved.