The kinetics of supercritical fluid extraction from vegetable raw materials in fixed beds was studied. The operational conditions used in the extraction of ginger oleoresin were pressures of 150, 200, and 250 bar, temperatures of 20, 30, and 40 degreesC, and a solvent flow rate of (5.6 +/- 0.3) X 10(-5) kg/s of CO2. A mathematical model obtained from the differential mass balance in the extraction bed was presented. This model considers the extract as a mixture of various groups of compounds, classified according to their chemical characteristics. The interfacial mass flux of each group of compounds was assumed to be described by one of the solutions of the logistic equation. The model was able to describe quite well the experimental results for ginger oleoresin extraction, considering the extract either as a single pseudocompound or as the sum of three groups of compounds. The overall extraction curves were fitted by both the proposed model and Sovova's model; the sum of square deviations was lower for the proposed model.