Inverse gas chromatography (IGC) has been used to measure the surface adsorption of some probes (n-alkanes on a series (n-C5 to n-C8) cyclohexane and benzene) on NaY and CaY zeolites. From the retention volumes at infinite dilution over a range of temperatures, the differential heat of adsorption (Delta H degrees), the standard free energy of adsorption (Delta G degrees), and the standard entropy of adsorption (AS') have been determined for the probes on the NaY and CaY zeolites. It was found that interactions of probes with CaY stronger than that on NaY. The dispersive (London) component of the surface free energies (y(s)(d)), has also been calculated. The dispersive components of the surface energies for CaY were found to be higher than the values for NaY. (c) 2005 Elsevier B.V. All rights reserved.