Abstract: The overall plate efficiency of vapor-liquid-liquid three-phase distillation was investigated in a sieve-tray Oldershaw distillation column of 50mm diameter . In froth flowregime , the effects on mass transfer of the operating conditions , e.g. vapor velocity and liquid to vapor loading ratio , and the physical properties of liquid phase , including surface tension , interfacial tension , dispersion viscosity , density , diffusion coefficient , relative volatility etc. , were systematically studied . The influence of the oil to water volume ratio on overall efficiency was also investigaed . Three-phase and two-phase distillation operations were compared in terms of plate efficiency . An analysis of the experimental results showed that the overall efficiency for three-phase distillation was lower than that for two-p hase distillation and interfacial tension and dispersion viscosity are the main influence factors . Finally , a correlation equation of overall efficiency for vapor-liquid-liquid three-pha se distillation in froth regime was obtained by regression of experimental data . This empirical correlation may be of some value in design and optimization .