The expressions of mass-transfer rate for membrane extraction through a rectangular module have been derived under cocurrent-flow, countercurrent-flow and cross-flow operation based on the modified correction-factor analysis. These expressions are explicit and the results can be readily calculated without using try-and-error method, which should be employed in the conventional correction-factor analysis for designing heat and mass exchangers. The correction factors for both cocurrent-flow and countercurrent-flow operations may be taken as unity when the logarithmic-mean concentration differences are properly selected. For cross-flow operation, the correction factors are function of flow rate, mass-transfer area, distribution coefficient and overall mass-transfer coefficient, and some values of them are given graphically. (C) 2007 Published by Elsevier B.V. on behalf of Taiwan Institute of Chemical Engineers.