The composition of humic acids (HAs) isolated from a South Moravian lignite deposit was examined via thermochemolysis and RuO(4) oxidation. The combination of thermochemolysis with TMAH and TEAAC shows that fatty acids were mostly in a "free" form, tightly trapped within the humic acid organic network. Humic acids contain also trapped hydrocarbons. The relative distributions of these compounds confirm their higher plant origin. RuO(4) oxidation resulted in a lipophilic fraction containing mainly fatty acids. The hydrophilic fractions released upon RuO(4) oxidation comprised mostly aliphatic C(2)-C(9) dicarboxylic acids and hydroxy acids related to short methylene bridges, to bridges between aromatic and/or oxygenated moieties such as aliphatic chains of ligneous units. (C) 2009 Elsevier Ltd. All rights reserved.