Densities of 1-butyl-3-methylimidazolium octylsulfate ([bmim][OcOSO(3)]) solutions in water and 1-propanol have been measured with an oscillating-tube densimeter at temperatures from 278.15 K to 328.15 K. From these densities, apparent molar volumes V-phi of [bmim][OcOSO(3)] in both solvents have been calculated, and its dependence on the molality has been treated with the Redlich and Meyer equation. Debye-Huckel limiting slopes for 1-propanol at working temperatures have been calculated, and apparent molar volumes of [bmim][OcOSO(3)] at infinite dilution V-phi(degrees) in both solvents have been evaluated. The partial molar volume at infinite dilution of [bmim][OcOSO(3)] in water is higher than in 1-propanol and augments when the temperature augments. On the other hand, the partial molar volume at infinite dilution of [bmim][OcOSO(3)] in 1-propanol decreases when the temperature augments. (c) 2005 Elsevier Ltd. All rights reserved.