The chemical structure of Estonian kukersite kerogen is evaluated using a simulation of C-13 MAS NMR spectrum. A reasonable fit to the experimental NMR spectrum is obtained by assuming a model of the geomacromolecule with empirical formula C421H638O44S4NCl and a set of structural elements comprising mainly alkylated phenolic structures particularly alkyl-1,3-benzenediols and condensed alicyclic rings. From the presented model new views are coming up on the carbon skeleton of kerogen and constraints on the phenol formation pathways in the retorting process, i.e. up to 80% of methylene groups in kerogen are located in aliphatic chains and the complicated mixture of phenols in the retort oil seems to result mainly from the thermal conversion of alkyl-1,3-benzenediol units originally present in kerogen. (C) 2002 Elsevier Science Ltd. All rights reserved.