An Illinois No. 6 coal preswollen in pyridine was allowed to undergo slow deswelling by solvent evaporation. The process was monitored by NMR and NMRI techniques in order to better understand coal’s macromolecular structure and mobility of solvent within the coal. Pyridine concentration profiles and spin-spin relaxation times measured by conventional H-1 NMR suggest that pyridine diffusion in the coal network during the initial stages of the deswelling process is Fickian and that the pyridine exists within two regimes of molecular mobility. NMR imaging perpendicular to and parallel to the coal bedding plane shows that the deswelling process follows nearly isotropic behavior. Once the pyridine concentration decreases to approximately 0.5 of the initial equilibrium concentration, a dramatic increase in the deswelling rate and decrease in pyridine concentration are observed, implying that a phase transition occurs at this point in the coal-pyridine system.