The simulated annealing algorithm is employed for the determination of the spatial distribution of a condensable adsorbate in reconstructed digital domains of mesoporous materials. The optimum configuration for a given degree of saturation is derived assuming that in equilibrium the total interfacial free energy reaches a global minimum value. The suggested approach is applied to reconstructed matrixes of Vycor and random sphere packs. Furthermore, the effective diffusivities of inert gases in the Knudsen regime are calculated in the resulting "dry" and "wet" images with a step-by-step random walk method. The predicted gas relative permeability curves are in satisfactory agreement with experimental results, confirming that the suggested combination of digital reconstruction and simulated annealing is a useful tool for the determination of the spatial distribution of a condensable sorbed phase in mesoporous solids.