The stability of the adsorbed monolayer, black lipid membrane (BLM) and bilayer vesicles is analysed by the use of the statistical mechanics. It is emphasized the effect of the concentration of the constitutive molecules of the membranes in the solutions on the stability of them. The BLM is shown to be in a metastable supersaturated liquid state for an appropriate condition. The bilayer vesicles are shown to be stable above the concentration at which the interfacial tension of the BLM diminishes to zero.
