The film model and penetration model predict different influences of binary interactions and thermodynamic non-idealities on gas-liquid mass transfer. Therefore, in case of concentrated systems, as often encountered in extraction and distillation processes, errors are made when the film model is used instead of the more appropriate penetration model. In this paper it is shown, for binary systems, that these errors can be reduced significantly, when the available mass transfer correlations are used to calculate the effective mass transfer coefficient from the effective diffusion coefficient instead of calculating the Maxwell-Stefan mass transfer coefficient from the Maxwell-Stefan diffusion coefficient. This is in contradiction with what is recommended in open literature.