Two highly volatile bituminous coal samples were characterized by adsorption and small-angle X-ray scattering (SAXS). The SAXS measurements were repeated on samples that had been brought to equilibrium at various relative pressures of carbon tetrachloride which has a similar electron density as the coals. The validity of this combined technique was ascertained by reconstructing the adsorption isotherms from the SAXS data. A theoretical approach connecting the two methods was considered, and simple formulae were derived. The reconstruction of the adsorption isotherm is influenced by several parameters. Adsorption in conjunction with SAXS can provide information on the pore structure, the adsorption mechanism, and the swelling of the solid matrix upon adsorption.