Water-oil-water (oily) liquid films appear between the droplets in water-in-oil emulsions. Here we report results from systematic experiments, aimed to clarify how several important factors affect the stability and drainage of such oily films, in the presence of the nonionic oil-soluble surfactant Span 80. These results reveal that: (1) At Span 80 concentrations around the CMC, the film lifetime coincides with the duration of film drainage. When the oily films reach a critical thickness of around 40 nm, unstable thinner black spots of thickness 1 h. This effect is explained with a mass transfer of molecules between the aqueous and the oil phases which keeps the oil films out of equilibrium for a long period. These results can be used to explain and control the formation and stability of water-in-oil emulsions, in the presence of nonionic oil-soluble surfactants.