Supercritical CO2 extraction of phenolic compounds from Zostera marina residues was optimized by developing a mathematical model based on mass transfer balances. A linear driving force model was applied considering model parameters such as solute concentration on the surface of the solid (C-s) and in the supercritical fluid phase (C-f), film mass transfer coefficient (k(f)) and molecular diffusivity (D-AB) and axial dispersion (D-ax) coefficients. Henry's law was used to describe the equilibrium state of solid and fluid phases. The results of the proposed model were compared to that of the experimental data in terms of transport properties and extraction yield at various temperatures (303.15, 323.15, 353.15 K), pressures (15,25,35 MPa) and co-solvent mass ratios (0, 10, 20%). The optimum parameters were elicited as 25 MPa, 353.15 K and a co-solvent ratio of 20% yielding 77.22 mu g g(-1) dry feed. The model satisfactorily described the extraction yield which can be used for scale-up purposes. (C) 2012 Elsevier B.V. All rights reserved.