The density of marine lipids in equilibrium with carbon dioxide (CO2) was determined using a view cell equipped with a novel spring balance based on Archimedes' principle. The densities of fish oil triglycerides (TG) and fish oil fatty acid ethyl esters (FAEE) were measured at pressures ranging from 0.1 to about 25 MPa and temperatures of 40, 55 and 70 degrees C. In the pressure and temperature ranges investigated, the density increased with pressure and decreased with temperature. The density increase from atmospheric pressure to about 25 MPa at temperatures of 40, 55 and 70 degrees C was 4.1, 3.2, 2.7% and 5.3, 4.0, 3.6% for TG and FAEE, respectively. Volumetric expansion of fish oil TG and FAEE saturated with CO2 was determined at 40 degrees C and pressures ranging from 0.1 to 22 MPa. With increasing pressure a relative volume change of up to 38 and 67% was observed for TG and FAEE, respectively. The density and volumetric expansion of lipids in equilibrium with CO2 are important for optimal design of high pressure processes involving mass and momentum transfer. (C) 2009 Elsevier B.V. All rights reserved.