Supercritical fluid chromatography-mass spectrometry (SFC-MS) and related techniques have been applied to the chemical characterization of a variety of fossil fuels, including diesel fuels, diesel fuel sediments, and petroleum- and coal-derived liquids and solids. Supercritical fluid chromatography can provide either high resolution or extremely rapid separation of complex fuel-derived mixtures. Insoluble sediments from marine diesel fuels can be extracted with polar supercritical fluids and the extracts directly introduced to a mass spectrometer for on-line characterization. Chemical class separations and mass spectrometric analysis of coal-derived liquids can be accomplished by utilizing high-performance liquid chromatography columns and a specially designed interface to the mass spectrometer. The development of polar supercritical fluids and Chromatographic columns for use with the polar fluids and the development (in addition to refinement) of the SFC-MS interfaces and capillary flow restrictors have been responsible for the successful application of SFC-MS and related techniques to the analysis of fossil-fuel-related materials.