In order to verify the possibility of using supercritical CO2 (SC-CO2) to concentrate polyunsaturated omega-3 fatty acids in the form of natural fish oil, experimental phase equilibrium data were measured for a CO2 fish oil system. Phase equilibrium was measured at temperatures from 301 to 323 K and pressures from 7.8 to 29.4 MPa, using the dynamic method. The oil solubility and fatty acid composition of the extracts were measured and these data used to verify CO2 Selectivity. The best operational conditions to fractionate the oil were 7.8 MPa and 301.15 K, although in all the conditions analyzed, eicosapentaenoic acid (EPA) could not be fractionalized. The equilibrium for a mixture of 50% fish oil and 50% babassu (Attalea funifera) fat was measured in order to understand how the fatty acid composition influenced the fractionation. It was observed that the solubility of the mixture was an average of the individual solubility values, and the composition of the extracts could be calculated from the individual solubility of each component. (C) 2008 Elsevier Ltd. All rights reserved.