Extraction of oil from crushed sunflower seeds with supercritical CO2 was performed at 280 bar and 40 degrees C on a laboratory apparatus of 0.15 x 10(-3) m(3) volume and on a pilot plant of 1.5 x 10(-3) m(3) volume. CO2 now rate ranged between 5 and 45 kg h(-1). To study the influence of the vegetable matrix on the extraction rate, a re-extraction experiment on the extraction product was also performed on the pilot scale apparatus. A mathematical model of the supercritical extraction process was developed on the basis of the experimental evidence. The equilibrium between the solids and the fluid phase appeared to be the controlling step during the extraction process. A simplified form of a sigmoidal-shaped equilibrium curve was adopted to fit the experimental data in the whole range of CO2 flow rates explored. The meaning of this nonlinear equilibrium relationship was also discussed.