Kerogen was treated for 24 h at temperatures of 250-700 degrees C and pressures of 500-1500 bar. Raman spectroscopic study of the run products documented systematic changes in both the first- and second-order spectral features with temperature and pressure. The micro-FTIR analysis of the kerogen treated showed that the presence of hydrogenated functional groups and importance of aromatic rings in the structures of the kerogen increased with temperature. An abrupt change in the chemical composition and structural state of the kerogen treated occurred at similar to 500 degrees C. (c) 2006 Elsevier Ltd. All rights reserved.