The determination CGC-FID of petroleum hydrocarbons in environmental samples is based on the assumption that the mass response of FID for hydrocarbons is constant and any petroleum distillation fraction can be used as a reference mixture for calibration purposes. It has been shown that the mass responses of FID for higher boiling hydrocarbons are not constant. Moreover, it was found that mass response calibration factors for petroleum oils boiling within an equal temperature interval differ more than 2.5 fold in dependence on the hydrocarbon group composition. In the CGC-FID determination of such petroleum hydrocarbons in environmental samples it is therefore necessary to use a reference material which provides not only chromatograms but also the group composition.