One goal of the Auto/Oil Air Quality Improvement Research Program (AQIRP) is the development of models which will predict the emissions characteristics of gasoline blends based on fuel composition. Speciation, the analysis of individual species in samples of gasoline or gasoline blend components, provides a key input to the development of such models (1)*(2)(3). Information on gasoline speciation has also been used to correlate fuel composition with combustion chamber deposits (4). The Fuels Analysis Sub-Committee of the AQIRP has implemented a capillary gas chromatography method for gasoline speciation. This method, commonly referred to as the Detailed Hydrocarbon Analysis method, or DHA, was cooperatively tested in seven laboratories with six samples. Examination of well resolved components in four of the six samples shows that the range of results obtained in the different laboratories typically varies by about 11% of the inter-laboratory mean. Replicate results obtained within single laboratories were found to vary by approximately 3% of the laboratory mean, though this repeatability varied from 1% to 7% for the different labs. Based on these data, modifications to improve method precision are proposed. A preliminary test of these modifications is currently in progress.