In the esterification process of long chain fatty acids with methanol, two liquid phases appear when excess methanol is added. Is this phenomenon available for the removal of water from the product mixture without any dehydrating agent and to increase the yield of the esters? The purpose of this paper is to answer the question experimentally and theoretically. The reaction and liquid-liquid distribution equilibrium have been measured at 73 +/- 0.5degreesC for oleic acid/methanol/methyl oleate/water system with a cation exchange resin as the catalyst. Furthermore, an algorithm has been proposed for calculating the equilibrium composition of single stage extraction-coupled reaction process. The algorithm was then applied to the calculation for the esterification process of oleic acid with methanol using the reaction equilibrium constant and the interaction parameters of UNIQUAC determined from the measured data. Both experimental and calculated results showed that water produced could be well removed from the reaction product in the two-phase region. Therefore, it is possible to increase the yield of methyl oleate by using excess methanol.