The petrography of rocks of the Upper Jurassic black shale Bazhenov Formation, which is considered as the main hydrocarbons source of the West Siberia, was studied by many researches. Despite the abundance of publications on the petrography of the Bazhenov Formation no commonly accepted classification has yet been elaborated. We have made an attempt to solve this problem on the strict formalized basis using chemical analyses of 100 samples of the Bazhenov rocks from its southeastern part. The main method of investigation was the cluster analysis (Ward's method) which was made on the content of 10 rock-forming oxides. Rocks with carbonate content more then 5 % were excluded from analysis. As the result of cluster analysis application Bazhenov Formation rocks were subdivided into two major groups which will be referred to A and B herein. The former group comprises five subgroups (1а-5а) and the second group consists of six subgroups (1b-5b). Further, the chemical analyses of each sample from each subgroup were recalculated into a mineralogical composition, and then mean mineralogical composition of each subgroup was calculated. The subgroups were named according to the standard rules. The rocks were named in accordance with their major rock-forming minerals (with contents above 5 %). It turned out, that group A contains rocks with quartz content more then 40 % (high-siliceous rocks), and group B - rocks with quartz content less then 40 % (low-siliceous rocks). Group A includes:1а. carbonaceous-clayey silicite;2а. pyritiferous-carbonaceous-clayey-cherty rock close to silicite;3а. carbonaceous-clayey silicite;4а. (clayey)-pyritiferous-carbonaceous-cherty rock;5а. Pyritiferous-carbonaceous-clayey-cherty rock; Group B includes:1b. Argillite siliceous;2b. Argillite carbon-siliceous;3b. Carbon-clayey-siliceous rock;4b. Argillite carbon-siliceous and siliceous;5b. Carbon-pyrite-clayey-siliceous rock;6b. Pyrite-carbon-clayey-siliceous rock.As can be seen, some subgroups have identical nomenclatures, but they differ from each other by the content of rock-forming minerals. In general rocks of group A differ from those of group B by elevated contents of organic carbon and contents of such elements as TiO2, MnO, MgO, CaO, Na2O and K2O. Reduced organic carbon content is observed in the most siliceous rocks of group A and most clayey rocks of group B. All these regularities of the rocks content of different sub-groups have the clear genetic interpretation.