This method is for determining the distribution of paraffins and naphthenes by carbon number, in hydrocarbon samples having an endpoint of 200°C or less (C3-C11). C12 at concentrations less than 3 can be determined. Olefins and aromatics interfere and must be removed prior to analysis by ASTM Method D 2002, D 2003 or other suitable technique. The lower limit of detection for a single carbon number hydrocarbon type is 0.05 mass- or LV-.