This is an automated method for determining the distribution of paraffins, naphthenes and aromatics by carbon number in hydrocarbon fractions having an endpoint of 200 C or less (C3-C11) (see NOTE). C12 paraffins and naphthenes at concentrations less than 3% can be determined. C9+ aromatics are reported as a group. Olefins, if present, are hydrogenated and the resultant saturates are included in the paraffin and naphthene distribution. The lower limit of detection for a single carbon number hydrocarbon type is 0.05 mass- or liquid volume (LV)-%.