Coal is one of the world's most chemically complex natural mixtures, whose composition varies with origin and age. Its combustion yields environmentally relevant "greenhouse" gases such as SOX and NOX. Here, for the first time, we apply electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to the analysis of Illinois No. 6 and Pocahontas No. 3 pyridine coal extracts. With the aid of Kendrick mass scaling, the elemental compositions can be sorted into different homologous series according to compound "class" (number of various heteroatoms) and "type" (rings plus double bonds). Many more species and classes were detected in Illinois No. 6 coal than in Pocahontas No. 3 coal. Illinois No. 6 coal contains mainly oxygen- and sulfur-containing classes; conversely, Pocahontas No. 3 coal contains nitrogen-containing classes. Both coals share O-2 and NO2 classes. Pocahontas coal exhibits much greater aromaticity (more rings plus double bonds) and less alkyl substitution (lower carbon number distribution) than Illinois No. 6, in accord with prior evidence that Pocahontas coal has higher carbon content (therefore higher rank) than Illinois No. 6 coal. Both the compositional information and the aromaticity data correlate well with known compositional and geochemical information.