This paper presents a mathematical model of the mass transfer in an industrial, solvent-based vegetable oil extractor. The model describes the countercurrent cross flows of the porous medium and liquid miscela, and some of the physical aspects of a real extractor: loading zone, drainage mechanism, oil loss, etc. A numerical algorithm is also developed based on the method of lines, and applied to the operational parameters of a real extractor. The numerical model is sensitive to the physical characteristics of the raw materials, the geometry of the extractor, and other factors. Experimental data on oil concentrations in the real extractor agree well with the model. (C) 2007 Elsevier B.V. All rights reserved.