The structure of five U.S. coals (three of low rank or sub-bituminous and two of high rank) has been investigated using reactivity criteria and spectroscopic methods. The results suggest that one of the high-rank coals PSOC 831 contains more cross-linking groups within its macromolecular structure than the other high-rank coal DECS 1.2. These cross-linkages help to explain some previously reported anomalous results resulting from reactions of PSOC 831 with hydrogen in the presence of MoS2. The DECS 9 and PSOC 1379 were shown to be typical low-rank coals and gave significant "guest"-derived materials (terpenoid and wax-derived hydrocarbons) from pyrolyses at 320 and 350 degrees C, and the sub-bituminous coal DECS 6 showed many structural similarities when compared with a range of other sub-bituminous coals from Central Queensland, Australia.