The relevance of the work is caused by the need to obtain information on thermal stability of organic nitrogen bases in resin components of the Upper Jurassic methano-naphthenic oil recovered from the Krapivinsk deposit located in the Tomsk Region to solve the problems associated with oil processing. The aim of the research is to obtain data on directions of thermal transformation of organic nitrogen bases in oil resins recovered from the Krapivinsk deposit. Methods: complexing, extraction, ¹H NMR spectroscopy, structural-group analysis, chromatography-mass spectrometry. Results. Based on the study of compositions and structures of organic nitrogen bases in the resins of the Krapivinsk oil before and after thermal treatment (450 °C, 30 min, inert medium), it was shown that at thermolysis under the selected conditions the partial destruction of high-molecular bases and complete loss of low-molecular bases occur. All bases in the thermolysed resins are the transformation products of high-molecular compounds in the initial resins. It was found that high-molecular compounds constituted a major part of the bases in the resins before and after thermal treatment, however their portion in the thermolysed resins was much lower. Thermally transformed bases have lower average molecular weights as compared with the initial ones. The compositions of the isolated compounds were studied by structural-group analysis and gas chromatography-mass spectrometry. It was shown that average molecules of the organic nitrogen bases of both resin types were composed of aromatic, naphthenic and alkyl fragments. In the average molecules of the compounds in the thermolysed resins the portion of aromatic carbon atoms was higher due to a decreased portion of naphthenic and alkyl carbon atoms. Alkyl derivatives of quinoline, benzoquinoline, dibenzoquinoline and azapyren, among which alkyl benzoquinolines predominate, are presented in the initial and thermolysed resin bases. An increased content of alkylquinolines is a feature of azaarenes in the thermolysed resins. Less developed alkyl substitution and a higher portion of low-molecular homologues are typical for thermally transformed structures.