Extraction of essential oils using supercritical CO2 was studied. A mathematical two-phase model was developed to simulate extraction yield at different operating conditions. Unsteady-state mass balance for solute in solid and in supercritical phases led to two partial differential equations that were solved numerically using a linear equilibrium relationship. The model has three parameters including mass transfer, axial dispersion and intraparticle diffusion coefficients. The last one was used as the model tuning parameter and the others were predicted applying existing experimental correlations. The model is able to show the influence of different process parameters such as particle size and flow rate on the essential oil recovery.