Solubilities of binary mixtures that contain a room-temperature ionic liquid and an organic solvent - namely, 1,3-dimethylimidazolium. methylsulfate, [mmim][CH3SO4], or 1-butyl-3-methylimidazolium methylsulfate, [bmim][CH3SO4] with an alcohol (hexan-1-ol, or octan-1-ol, or nonan-1-ol, or decan-1-ol), or an ether (dipropyl ether, or dibutyl ether, or methyl-1,1-dimethylethyl ether, or methyl-1,1-dimethylpropyl ether), or a ketone (pentan-2-one, or pentan-3-one, or hexan-2-one, or heptan-4-one, or cyclopentanone) -have been measured by a visual method from T = 270 K to the boiling temperature of the solvent. The (liquid + liquid) equilibria curves were predicted by the COSMO-RS method. For [bmim][CH3SO4], the COSMO-RS predictions correspond better with experimental results than do the predictions for [mmim][CH3SO4]. Complete miscibility has been observed in the systems of [mmim][CH3SO4] with water and with alcohols ranging from methanol to octan-1-ol and that of [bmim][CH3SO4] with water and with alcohols ranging from methanol to decan-1-ol at the temperature T = 310 K. (C) 2005 Elsevier Ltd. All rights reserved.