A single parameter model was earlier presented by Bhowal and Datta for prediction of the extraction rate of weak acids/bases by a liquid surfactant membrane. This parameter represents the fraction of solute diffusing into the emulsion globule that will be converted into reaction product by a reversible reaction in the internal droplets and was taken to be a constant for all systems. A useful generalized correlation has been developed in this work for calculation of the said parameter by regression as a function of the physical parameters and experimental conditions of the system. The validity of the correlation has been checked through comparison with the predictions of the reversible reaction approach of Bunge and Noble. The parameter value obtained from this correlation gave better estimations of the extraction profiles than those obtained assuming it to be a constant.