The technique of IR spectrometry was applied to the systematic analysis of the group composition of unfractionated oils from Jurassic deposits in southeastern West Siberia. The existence of three types of oils was revealed: methane, methane-naphthenic, and naphthenic-methane. The territorial and stratigraphic zoning of their occurrence was performed. The characteristic features of the composition of each type of oils were determined, and possible factors facilitating their formation were considered.