A sulphate lignin and humic acids of 5000-year-old peat, brown coal and black coal were subjected to cupric oxide oxidation. The compounds identified by GC-MS were lignin-derived phenolics, benzenecarboxylic acids and aliphatic mono- and dicarboxylic acids. Two lignin-derived phenolics, p-hydroxybenzoic acid and vanillic acid were common to all matrices. The results showed lignin to be one of the source materials in humification and coalification processes. Its importance in humification should not be exaggerated, however. Additional research is required to confirm whether the unsaturation of peat HA is mainly olefinic, as suggested by this study, or mainly aromatic.