The study deals with experimental verification of the various calculational methods proposed in the literature for multicomponent systems in which nonequimolar counterdiffusional mass transfer takes place. The experiments were done using the systems isopropanol-water-air and isopropanol-water-helium. The measurements were performed at the laminar downflow of the liquid phase (Re = 150-600) and the turbulent flow of the gas (Re = 3000-10,000). The results obtained were compared with those predicted by the various mathematical models which either include or neglect the effect of diffusional cross-effects on mass transfer rate. The neglecting of the cross-effects leads, in all cases, to considerable discrepancies between the predictions of the models and the experimental results. The diffusional cross-effects for the ith component are the largest when the ratio of the fluxes N-j/N-i is large, and when the binary diffusion coefficients for this component differ considerably from one another.