Effective diffusion coefficients (D-ef) and mass transfer coefficients (k(m)) in essential oil extraction processes from vegetal porous matrices using high-pressure carbon dioxide have been determined. The experimental data available for these calculations are extracted mass curves as functions of time for the extraction process of lemongrass essential oil (Cymbopogon citratus Staupf) using supercritical carbon dioxide as solvent extracting fluid. The mathematical model employed is based on Fick's second law, which has been solved using the finite element method and computer programs specially designed to evaluate the transport properties D-ef and k(m). A set of routines based on the modified Marquardt method to evaluate the optimum values of such properties were written and coupled with the finite element method code. The results show that the model employed and the computer programs developed are adequate to evaluate the transport properties and the extraction curves. Copyright (C) 2008 John Wiley & Sons, Ltd.