Prebiotic carbohydrates are defined as non-digestible carbohydrates that beneficially affect the host by selectively stimulating the growth and/or activity of a limited number of bacteria in the colon. The present study is focused on two prebiotic ketosugars: tagatose and lactulose, which are currently obtained by alkaline isomerization of their respective aldoses-galactose and lactose. It is a part of a broader research devoted to examining the possibility of complex solid carbohydrate mixtures fractionation using supercritical carbon dioxide and alcohol-type cosolvents. We report new experimental solubility data of tagatose, galactose, lactulose and lactose in supercritical carbon dioxide with ethanol:water (95:5, v/v) used as a cosolvent at T = (60 and 100) degrees C, P = (10-30) MPa and cosolvent content from 6 to 21% (w/w). The solubility measured was in the range (0.02-1.09) mg g(-1). Additionally, the experimental data was correlated using the Soave-Redlich-Kwong cubic equation of state with the modified Huron-Vidal second order (MHV2) mixing rule. The latter employs the mS-UNIFAC, which introduces two new groups in the original UNIFAC parameter matrix to represent the sugar molecules. (C) 2008 Elsevier B.V. All rights reserved.