This paper reports densities of aqueous solutions of ionic liquid (IL) 1-methyl-3-ethylimidazolium ethyl sulfate (EMISE) that were measured gravimetrically at temperatures (278.15 to 333.15) K. The values of the apparent molar volume, V-phi(B) and partial molar volume, (V) over bar (B), were determined and apparent molar expansibilities E-phi = ((partial derivativephiVB)/(partial derivativeT))(p) of EMISE and the coefficients of thermal expansion of the solutions, alpha, were calculated. The values of the apparent molar volume, OVB, were fitted by the method of least-squares to a Pitzer's equation to determine the parameters, beta(MX)((0)V), beta(MX)((1)V), and C-MX(V). (C) 2004 Elsevier Ltd. All rights reserved.