Two mathematical models, Sanchez-Lacombe equation of state and the Perturbed-Chain Statistical Associating Fluid Theory were applied for modelling the phase equilibrium for the poly(L-lactide)-CO2 and poly(D,L-lactide-co-glycolide)-CO2 Systems. Aspen Polymer Plus software was used. The results were compared with previously obtained experimental values for solubility. The solubility of scCO(2) in the two biodegradable polymers was calculated for three different temperatures (308,313 and 323 K) in the pressure range (10-30 MPa). The characteristic parameters for the components and the binary interaction parameters for the models were optimized in order to obtain the best fit between the estimated and the experimental gas solubility data. The results suggest that both SL EOS and PC-SAFT are reliable models in describing the phase equilibrium of the PLLA-CO2 and PLGA-CO2 systems at the proposed working conditions. (C) 2009 Elsevier B.V. All rights reserved.