Chemical changes in the structure of kerogen during simulated thermal maturation were investigated by solid-state C-13 NMR spectroscopy. The spin counting technique was used to evaluate the share of "observable'' carbon atoms with increasing hydrous pyrolysis temperature. The obtained one-dimensional CP-MAS spectra showed that up to 50% of ether bonds were destroyed during the initial stages of sample heating. In spite of the loss of a significant part of alkyl chains, kerogen remained aliphatic. The aromatic structure of kerogen underwent considerable changes: two-dimensional H-1-C-13 heteronuclear solid-state NMR (HETCOR) spectra showed that in the process of hydrous pyrolysis, the redistribution of carbon atoms took place - branched aromatic carbons transform into bridgehead aromatic carbons. (C) 2013 Elsevier Ltd. All rights reserved.