Californium plasma desorption mass spectrometry (PDMS) has been used to analyze heavy distillation residues obtained from direct coal liquefaction processes. The characteristics of the Cf-252 PDMS technique for the analysis of these nonpolar materials were determined, especially the efficiency with which molecules of different chemical type are ionized and detected. The molecular weight distributions of several THF-soluble portions of nondistillable residual materials (850 degrees F + "resids") obtained from the Wilsonville pilot plant were determined. These data are compared to results obtained by field ionization mass spectrometry (FIMS) and gel permeation chromatography (GPC). In general, number-average molecular weights for all three techniques agreed well. The molecular weight distributions for these resids produced under a range of conditions are quite similar. The separation of the resids into chemical classes by medium-pressure column chromatography (MPLC) on silica gel is irreversible.