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 orless (C3 through C11). C 12 paraffins and naphthenes atconcentrations totaling less than 3% can be determined. Olefinsmust be less than 2%. C6 minus can be reported either individuallyor by carbon number. C7 through C12 paraffins and naphthenes aredetermined by carbon number. Aromatics through C10 can bedetermined individually or by carbon number with C11 aromaticsdetermined as a composite. Olefins are reported undistributed.Results are reported in mass-percent (mass-%) or liquidvolume-percent (LV-%).