Pyridine sorption isotherms were determined for three Argonne Premium coals at 50 degrees C. It is proposed that the isotherms are best interpreted in terms of a dual-mode sorption model originally developed to explain sorption of vapors into glassy polymers. This model considers two different populations of sorbed gas; one is dissolved:into the polymer and is described by Henry’s law (i.e., sorption is linear with pressure) while the second population is considered to occupy unrelaxed free volume (micropores) within the polymer and is described by a Langmuir isotherm. We propose that the high-pressure linear portion of the pyridine isotherms for two coals represent dissolution of pyridine in the coal matrix and that the low-pressure regions represent primarily adsorption;into micropores. The intercepts of the linear portion thus represent micropore volume accessible to pyridine. The pyridine-extracted coals all show a dramatic increase in intercept value, suggesting that pyridine extraction creates new micropores. O-alkylation with bulky alkyl groups yield reduced intercepts, which correlate with. the size of the added alkyl group. It is suggested that the added alkyl groups occupy micropores in the structure.