Capillary condensation is associated with a decrease of the surface energy at the interface between the pore walls and the sorbate. This decrease is related to the difference in the free energy of the sorbate between the occluded state and the free liquid state. An equation based on this relation is derived. The equation is applied to condensation in pores in which only a part of the pore wall adsorbs, like in the case of the adsorption of water by microporous active carbons. The condensation pressure is determined in these systems by the parameter r(k)/Y, where r(k) is the width of the core of the pore and Y is a function of the fraction of the pore walls that adsorbs.