This study deals with the enzymatic modification of vegetable oils with the help of a new reactor design. Basically, the new reactor is a porous membrane contactor along and through which substrates are flowing. It is constituted from an enzymatic membrane and uses supercritical carbon dioxide (SC CO2) to fluidity the highly viscous substrates. The interesterification between castor oil triglycerides and methyl oleate catalysed by a lipase was chosen as a model reaction. It was preliminary tested and characterized in a batch reactor. Then the feasibility of the new process was demonstrated on a cross-flow filtration unit operating under SC CO2 conditions. The stability of the immobilized enzymes was checked and the influence of the transmembrane pressure on the reaction rate was observed. (C) 2004 Elsevier B.V. All rights reserved.