Densities of some aqueous ionic liquids containing alkyl sulfate anions, 1-ethyl-3-methylimidazolium methyl sulfate. 1-hexy1-3-methylimidazolium methyl sulfate, and 1-hexy1-3-methylimidazolium ethyl sulfate solutions were measured at T = (298.15-328.15) K and at atmospheric pressure. The apparent molar volumes at infinite dilution were found by extrapolation to infinite dilution with using Redlich-Mayer and Pitzer equations. The apparent molar volumes at infinite dilution were used to obtain information about solute-solvent and solute-solute interactions. The temperature dependence of apparent molar volumes were used to calculation of apparent molar expansivities and the Hepler's constant values, (partial derivative V-2(phi)0/partial derivative T-2)(P). The Hepler's constant values were found very small negative which indicating the ionic liquids under study are predominantly a structure breaker due to hydrophobic hydration of ionic liquids in water. The results were discussed in terms of alkyl chain length and anion size on the volumetric properties on the studied ionic liquids. (c) 2011 Elsevier B.V. All rights reserved.