Phase behavior of solutes in supercritical fluids can be modified by the addition of small amounts of cosolvents. The addition of a cosolvent may increase solubility selectively or non-selectively. This solubility enhancement results from an increase in solvent density and/or intermolecular interactions and can be used to improve the feasibility of a process by improving solvent loading and/or selectivity. The effects of cosolvent addition on the solubility behavior of solutes and on various aspects Of SCCO2 processing were assessed with special emphasis on lipids. The cosolvent effect in ternary systems of lipid components (fatty acids (palmitic, stearic and behenic acids), beta-carotene, squalene, stigmasterol), cosolvent (ethanol) and SCCO2 was quantified as the ratio of solubility obtained with cosolvent addition to that without a cosolvent. The effects of operating conditions, cosolvent concentration, and cosolvent and solute properties on the cosolvent effect were identified. Cosolvent effects for these solutes were compared and implications for fractionation were noted. Solubility enhancement was observed for all lipid systems, but to different extents. Cosolvent effect for fatty acids decreased with pressure. Specific intermolecular interactions (H-bonding) between the fatty acids and ethanol contribute significantly to the cosolvent effect and can be exploited to increase selectivity of a fractionation process. Study of the use of cosolvents for any process should entail a case by case analysis, which takes into account the effect of the cosolvent not only on the solubility behavior but also on mass transfer properties, process design, quality of the extract and/or the residue, post processing steps such as compositional analysis and cost. (c) 2005 Elsevier B.V. All rights reserved.