Inverse gas chromatography at infinite and finite surface coverages was applied to evaluate the surface properties of an iron-modified sepiolite sorbent, Fe-sepiolite. The adsorptions of different nonpolar and polar probes were measured in the infinite-dilution regime, in the temperature range 483-513 K. For the organic probes used, the thermodynamic parameters (free energy, enthalpy, and entropy) of adsorption and the dispersive and specific components of the free energy of adsorption were determined and are discussed in terms of specific reactions that can occur on the adsorbent surface. Following the approach of Gutmann (The Donor Acceptor Approach to Molecular Interactions; Plenum Press: New York, 1978), acid/base surface characteristics were determined. The adsorption isotherms of n-hexane, benzene, chloroform, and tetrahydrofuran were used to estimate the specific surface areas, isosteric heats of adsorption, and adsorption energy distributions for the adsorption of organic molecules.