In this work, a simple model is provided which accounts for any value of distribution coefficient of a solute, to describe the mass transfer for a batch process of extracting the solute between two immiscible fluids. A Lewis cell of constant interfacial area and a stirring tank were employed as the apparatuses for measuring the mass transfer rates of a solute between two immiscible phases. The model, which was based on the two‐film theory to determine the rate of mass transfer of solute across the interface, and the equilibrium concentration of solute at the interface, was derived and used to express the extraction of phenol. Experimental work, in which phenol was extracted from the aqueous phase to the organic phase by trioctylamine sulfate salts (TOA salts) dissolved in trioctylamine (TOA), was conducted to obtain the mass transfer coefficient. The effects of the operating conditions in a constant interfacial area cell and in the stirring tank are both discussed.