Analysis of the tri- and tetraaromatic hydrocarbon fractions of a brown coal sample from the Latrobe Valley, Victoria, Australia indicate the predominance of pentacyclic hydroaromatic components. Many of these have not been previously reported in the literature, but are obviously diagenetically related to triterpenoids naturally occurring in the biosphere. The components whose molecular structures have been confirmed, together with those for which tentative structural assignments are given, offer strong support for a theory of progressive diagenetic aromatization of C-3 oxygenated triterpenoids, commencing from ring A. Other compounds present in smaller amounts suggest that 1,2-methyl shift reactions also occur prior to or during aromatization. There is a notable absence of polycyclic aromatic hydrocarbons (PAH's) which can be diagenetically related to the steroid or extended-side-chain hopane skeletons.