The supercritical fluid extraction of oil from milled celery seeds, using CO2 as a solvent, is presented in this study. The effect of the process parameters - pressure and temperature of extraction, particle size of celery seeds and flow rate of CO2 - on the extraction rate was examined in a series of experiments. The results indicated a significant increase in extraction rate with increase of pressure or decrease of the particle size of celery seed. A similar effect was observed with the increase of the solvent flow rate and decrease of temperature. The experimental data were described by an empirical model and two mass balance models: (1) a simplified model, which takes into account only the time dependence of the extract concentration in the two phases and is coupled with various equilibrium relationships, and (2) an extended Lack's model. The correlation results were satisfactory especially for the mass balance models, which account for the double regime - solubility and diffusion controlled regimes - of the extraction. (C) 2000 Elsevier Science B.V. All rights reserved.