To investigate the possibility of carrying out a reaction in the medium ionic liquid/supercritical CO2 as mixed solvents, the solubility of carbon dioxide in the mixture 1-butyl-3-methylimidazolium tetrafluoroborate (bmim[BF4]) + 1-(4-isobutylphenyl)-ethanol has been investigated. Measurements were carried out in a Cailletet apparatus at pressures up to 14 MPa. In the temperature range from 278 K to 368 K, the solubility of CO2 in the mixture was found to slightly decrease in comparison with the solubility in pure bmim[BF4]. The effect of the solute nature has been investigated by comparing the results with two other ternary systems previously investigated, with 4-isobutylacetophenone and I-phenylethanol as organic solutes. The results have shown that even similar molecules can affect the solubility of CO2 in the bmim[BF4] + organic mixture in different ways, with higher solubility of carbon dioxide for ketones as solute rather than an alcohol and that the addition of an alkyl group to solute molecules with the same functional group will most likely facilitate carbon dioxide solubility. (C) 2008 Elsevier B.V. All rights reserved.