A comparative IR spectroscopy and pyrolysis gas chromatography study of the changes in chemical structures was performed for the following carbonization series of solid bitumens: asphalt --> asphaltite --> kerite --> anthraxolite. It was found that exposure of solid bitumens to high temperatures (500degreesC) leads to a significant change in their chemical composition and structure. In the structural aspect, the alteration is related to carbonization processes. High temperatures result in the volatilization of decomposition products containing lighter molecules, and the nonvolatile residue is enriched in carbon. Thus, the asphaltic-resinous components of solid bitumens are polymerized and transformed into the carboid fraction.