A novel experimental approach is proposed to investigate the influence of interfacial convection on liquid-side mass transfer. Specifically, a binary liquid mixture (water and isopropanol) is evaporated from a porous obstacle into inert gas (air). The change of liquid bulk molar fraction with changing amount of liquid (concentration curve) is observed. The porous obstacle is a plate with parallel planar gaps, or a packed bed of spherical particles, both completely filled with the liquid. Without interfacial convection, that is, for the undisturbed state of the system, the liquid is quiescent and evaporation should be nonselective. Consequently, measured selectivities not only prove the existence of interfacial convection, but also give the opportunity of evaluating liquid-side mass transfer coefficients and enhancement factors for the disturbed state of the system. This evaluation is conducted with the help of a one-dimensional model for mass and heat transfer. If applied to the undisturbed state of the system, the same model provides driving density and molar fraction differences in the form of Rayleigh and Marangoni numbers. It is shown that the extent of interfacial convection can be controlled by operating parameters such as the gas bulk temperature, whereas it also depends on structural parameters such as gap width or particle diameter. Thermally driven and molar fraction driven Rayleigh and Marangoni convection may coexist. With the described method much higher enhancement factors than ever previously reported could be detected. The dependency of such enhancement factors on the Rayleigh or Marangoni number is considerably stronger than reported in the literature. Some aspects concerning the consideration of liquid-side heat transfer or permeability and structure of the medium are discussed, and nonselective experiments corresponding to stable configurations are identified. First attempts toward correlation of the results are outlined, along with the potential of the method for future research. (c) 2005 American Institute of Chemical Engineers.