An analytical program has been developed to identify approximately 225 compounds that may exist in automotive gasoline engine exhaust and evaporative emissions. This method combines five separate gas chromatographic analyses and a high performance liquid chromatographic analysis. It provides for independent determinations of benzene, toluene, ethers, and alcohols to minimize interferences during the capillary separations. Also provided is the determination of 2,2,3-trimethylpentane using the toluene analysis, instead of providing only a combined value for these coeluting compounds.The data from these several separate analyses are combined to provide a final speciation report giving mg/mile values for each compound or compound group. This type of data is used to study the effects of gasoline compositional changes on emissions and on ozone formation, especially when combined with the speciated analysis of the gasoline.