Monomolecular films based on poly(styrene-allylalcohol), PSAA, (mean molecular weight = 1500 g/mol) have been studied by means of the Langmuir technique. PSAA forms a highly compressible film which is not affected by changes in subphase pH. Addition of hexadecylaniline (HDA) and eicosylamine modifies the PSAA film. PSAA/HDA films obey additivity at low surface pressures, but not at pressures exceeding 12 mN/m and at low subphase pH. The mixed monolayers of PSAA and HDA have larger collapse pressures than the single component films. All the unionized films show a relaxation behaviour characteristic for polymer reorganizations in monomolecular films. Addition of 1-butanol and benzylalcohol to the subphase reveals substitution effects with regard to spreading as well as specific incorporation into the films. Model films of PSAA containing additives reproduce to essential parts the film behaviour of the previously investigated, interfacially active fraction of authentic crude oils. There seems to be small deviations with regard to maximal compression and surface activity between authentic crude oils and PSAA-based model systems.