The potential use of gas chromatography/electron ionization mass spectrometry with high-energy electrons for detailed type analysis of heavy distillates and residual petroleum products has been shown. The method is based on the selection of characteristic ions corresponding to certain structural groups in the mass spectra presented as tables of homologous-series ions. In a set of ion mass chromatograms of a homologous series, these ions produce chromatographic peaks that can be represented as sections of a certain three-dimensional pseudo-peak. These three-dimensional peaks characterize both mass and retention time intervals for characteristic ions of compounds of a particular type. The overlap of the characteristic ion peaks of a given type of compounds with other types is much less than in the absence of chromatographic separation, since it is limited to compounds that elute in the given interval of retention times. The contribution of each group of compounds to the total ion current is determined from the sum of abundances of characteristic ions with allowance for the overlap of the mass spectra and differences in the ionization efficiency. The type analysis by this method can be performed without preliminary separation into saturates and aromatics.