This method is a procedure for calculating paraffin, olefin, naphthene and aromatic hydrocarbon types in hydrocarbon fractions, such as reformer feeds and reformates, having endpoints of 200°C or less (C3 through C11). C12 paraffins and naphthenes at concentrations totaling less than 3% can be determined. Olefins must be less than 2%. C8 minus paraffins and naphthenes are reported individually. C9 through C12 paraffins and naphthenes are determined by carbon number. Aromatics through C10 are determined individually with C11+ aromatics determined as a composite. Olefins are reported undistributed. If analysis by carbon number only for all hydrocarbon types over all carbon number ranges is sufficient, use ASTM Method D6839, "Hydrocarbon Types, Oxygenated Compounds, and Benzene in Spark Ignition Engine Fuels by Gas Chromatography." Results are reported to the nearest 0.01 mass-%. Conversion to liquid volume-percent (LV-%) is described in the Appendix.