Measurements of osmotic coefficients of BmimCl (1-butyl-3-methylimidazolium chloride) and HmimCl (1-hexyl-3-methylimidazolium chloride) with ethanol and EmimEtSO(4) (1-ethyl-3-methylimidazolium ethylsulfate) and EmpyEtSO(4) (1-ethyl-3-methylpyridinium ethylsulfate) with water at T = (313.15 and 333.15) K are reported in this work. Vapour pressure and activity results of the studied binary systems are obtained from experimental measurements. The results for the osmotic coefficients are correlated using the extended Pitzer model modified by Archer and the modified NRTL (MNRTL) model. The standard deviations obtained with both models are also given. The parameters obtained with the extended Pitzer model of Archer are used to calculate the mean molal activity coefficients. (C) 2008 Elsevier Ltd. All rights reserved.