One of the reasons problems arise in the design of extraction equipment is an unsatisfactory knowledge of the mechanisms responsible for the transport of components from the bulk of one phase across the interfacial area into the bulk of the other contacting phase. An investigation was carried out on mechanisms relevant for mass transfer, the importance of multicomponent effects in liquid-liquid extraction and also which models are suitable for describing mass transfer. For this, experiments were performed in a countercurrent spray column with the system ethylacetate-acetone-water. The saturation of the feed phases, the extraction factor and the direction of mass transfer were varied. When phases fed into the column are saturated, both phases change their concentration along the binodal line. When the phases are initially unsaturated, both extraction trajectories approach the binodal line. Comparing the experimental concentration profiles with simulation results, it is shown, that in the area of undersaturation, extraction trajectories can be described only if the complete matrix of multicomponent diffusion coefficients is known and the effects of diffusive coupling are taken into account. When mass transfer coefficients are calculated at bulk concentrations, the achieved results are closer to the measured extraction trajectories than in the case where they are calculated depending on interfacial concentrations.