We have correlated simultaneously experimental data for osmotic and activity coefficients of 122 aqueous solutions of pure electrolytes at 298.15 K using a modified Pitzer model. We have compared our results with well-known models such as the Pitzer and Lietzke models. For electrolytes with monovalent ions, the modified model compares favorably to the original Pitzer and Lietzke models. For electrolytes without monovalent ions such as 2:2 and 3:2, the Pitzer equation correlates better at the expense of using four adjustable and three fixed parameters whereas the modified model requires only three adjustable parameters.