The adsorption of non-ionic, anionic and cationic surfactants on a stationary mercury electrode from aqueous solutions of a supporting electrolyte is discussed with respect to phase transformations in the adsorption monolayer, the determination of adsorption parameters and outer Helmholtz potentials. Investigations of the stability of thin liquid films, formed from solutions of these surfactants between a mercury electrode and a hydrogen bubble reveal certain peculiarities. The latter are explained by the assumption of the existence, in some cases, of a hydrophobic component of the of the disjoining pressure in the films, with the estimation of the corresponding hydrophobic force constant.