Thorium oxide is an excellent stable model substrate for development of sorption models for definitive evaluation of surface area and porosity. The physical adsorption isotherms for argon on thorium oxide surfaces have been reported in the literature with minimal interpretation with respect to the energy and mechanisms of the sorption processes. The data are analyzed in terms of the AutoShielding Potential (ASP) concepts to reveal argon physical adsorption on hydrated surfaces as contiguous monolayer-multilayer formation. Successively more energetic monolayer formation is observed when the screening surface hydration is removed in a vacuum at elevated temperatures. Argon multilayer formation is affected to a lesser degree by dehydration. The ASP methodology is unexcelled in defining physical adsorption for delineating structural and porosity factors as revealed in the sorption isotherms.