A suite of 24 Australian coals ranging from semianthracite to brown coals, and the corresponding asphaltenes and residues resulting from hydroliquefaction studies have been characterized by the Fourier Transform Infrared technique. The spectral data in the carbon-hydrogen stretching region were used to determine aliphatic and aromatic contents of the samples. Information on the aliphatic and aromatic structures of coals was obtained by investigating the relationship of the aliphatic and aromatic hydrogen contents in coals and products to the coal H/C atomic ratio and to the liquefaction data. The results strongly support the guest-host structure for the brown coals. The variability in the structures observed for the higher rank coals supports the conclusion that such coals have a more complex macromolecular skeleton than the brown coals.