The effect of surfactants on interfacial mass transfer in binary liquid-liquid systems has been investigated experimentally using the Schlieren and the Mach-Zehnder optical techniques. The Schlieren optical apparatus enabled the observation of the stability of the interfaces during the mass transfer process in the organic-aqueous systems selected, when the aqueous phase was ＇clean＇ or ＇contaminated＇ by selected surfactants. The Mach-Zehnder interferometer was used to measure molar fluxes in the same liquid-liquid systems. Results have shown that the presence of an ionic surfactant in the aqueous phase could either initiate or increase Marangoni convection and enhance (up to seven times) the measured molar fluxes. Slight decreases in molar fluxes were measured for the cases where Marangoni convection was observed to have been dampened by the addition of a non-ionic surfactant. The possibility is thus raised for the manipulation of interfacial stability, through the addition of a surfactant to induce or inhibit Marangoni convection, for the improved design and understanding of interfacial processes. (C) 2000