Thermal decomposition behavior was investigated by use of stepwise pyrolysis-gas chromatography for four oil shales (Colorado, Condor, Maoming and Timhadit oil shales from USA, Australia, China and Morocco, respectively) and their kerogen concentrates. It was revealed that product distribution was dependent on pyrolysis temperature for all the kerogens examined as well as for the oil shales. Isoprenoid hydrocarbons were mostly generated at 430-degrees-C from all samples examined, while the majority of 1-alkenes and n-alkanes were generated at 470-degrees-C and/or 520-degrees-C. Yields of benzene, toluene and xylenes did not significantly change through the stepwise pyrolysis. Based on the pyrolysis behavior, the carbon skeleton structure of kerogen is discussed.