The volumetric behavior of ethyl esters and fish oil ethyl eaters in the presence of supercritical CO2 was studied with a newly designed flow apparatus. Pure eaters studied were ethyl acetate (C2), ethyl octanoate (C8), ethyl laurate (C12) and ethyl linoleate (C18:2). Fish oil ethyl esters were derived from esterification with ethanol. Conditions were CO2 at 313.2 K over the pressure range of 0.1-25 MPa and over the full range of single phase compositions. The density data were interpreted in terms of swelling factors, V-mix/V-ester. It was found that the swelling factors over the full range of compositions at a given pressure could be made to collapse into a single curve by using weight fraction instead of mole fraction. Further, the Soave-Redlich-Kwong equation of state was found to provide prediction of the swelling factors to within 3.0% average error or correlation to within 1.1% average error. Supercritical CO2 + fish oil mixtures were found to show the same swelling behavior as supercritical CO2 + ethyl esters.