We introduced in (2) and (3) the excess surface work (ESW) to describe adsorption isotherms of nonporous materials and of a single phase over the complete pressure range. In this paper this model is extended successfully to adsorption isotherms of porous and finely dispersed materials. In this case capillary condensation may occur and the excess surface work yields more than one minimum. By linearizing the corresponding integral form and calculating the parameters, it is now possible to describe the complete adsorption isotherm as for the simple case of nonporous systems.