The Π-A isotherms and relaxation behavior of monomolecular films at the air/aqueous solution interface of a copolymer of styrene and allylalcohol (PSAA), mean molecular weight 1500 g/mol) have been investigated as a function of the subphase surfactant concentration. The surfactants were sodium dodecylsulphate (SDS), cetyltrimethylammonium bromide (CTAB) or cetylpyridinium chloride (CPC). At low surfactant concentrations (≲0.3 CMC), the PSAA film is penetrated by surfactant molecules and undergoes a relaxation consistent with conformation changes of the polymer without dissolution into the subphase. At higher concentrations (≈ CMC) the PSAA film is lsowly dissolved into the subphase; Π-A isotherms show a plateau and the films relax by a gradually decreasing surface area. The dissolution of PSAA is probably brought about by adsorption of surfactant molecules onto the polymer chain, giving rise to a water-soluble polymer-surfactant “complex” of poly-electrolyte nature. At medium concentrations, hydrophobic interactions between the neutral polymer and the ionic surfactant increase the hydrophilicity of the film and, thereby, probably lead to the formation of loops of polymer segments into the subphase. All the surfactants seem to interact with the PASS film in similar ways. PASS monolayers are good model systems for emulsion-stabilizing monolayers in North Sea crude oils. The monolayers of both the PSAA and the interfacially active crude oil system respond similarly to the presence of ionic surfactants, indicating anogous dissolution mechanisms. Thus, specific surfactant-monolayer interactions of the type observed will be of importance for an understanding of water-in-crude oil emulsion stability.