Single drop mass transfer data have been obtained for the ternary and quaternary systems toluene-acetone-water and toluene-acetone-phenol-water. The addition of surfactant was also made for some experiments. The results were assessed using a simple single solute mass transfer model and a non-equilibrium model based on the Maxwell-Stefan equations. In both cases allowance was made for the effects of interfacial contaminants or solutes by using empirical correlations for the mass transfer coefficients which were developed to take contamination into account. The non-equilibrium model rate-based calculations gave different results to the single solute model in the case that the two main solutes were undergoing simultaneous mass transfer. It is considered that the phenol is sufficiently interfacially-active to behave like a surfactant and this has major impact on mass transfer coefficients and hydrodynamic assumptions made for the non-equlibrium model. The concentrations of solute were relatively low and the non-equilibrium model did not indicate any notable degree of interaction of the mass transfer coefficients of the two main solutes. Chemical systems with much higher solute concentrations need to be investigated. (C) 2002 Elsevier Science B.V. All rights reserved.