The time separation of experimental surface energy on Pt-Rh bimetallic catalysts, together with the time-independent rate constants for adsorption and desorption of O-2, CO, and CO2 on them, is described, applying the reversed-flow version of inverse gas chromatography. The standard free energy of adsorption DeltaG(circle minus) and its probability density function over time, together with the geometrical mean of the London parts of the total surface free energy (gamma(1)(L)gamma(2)(L))(1/2) of the adsorbed probe and the solid surface, accompanied by the relevant probability density functions over time are also calculated. The time-resolved phenomena lead to quite varying values of DeltaG(circle minus), (gamma(1)(L)gamma(2)(L))(1/2), and the distribution functions as time passes, their maximum values being given by the catalyst containing a Pt:Rh = 3:1 weight ratio of the active phase for all adsorbed gases. The conclusion is reached that the surface energy measured as described can be used as a good measure for catalyst characterization. (C) 2003 Elsevier Inc. All rights reserved.