The thermodynamic properties of the binary aqueous solutions of 183 electrolytes at 25 °C and 1 bar have been fitted using a standard form of the Pitzer equations. Where possible, all thermodynamic properties have been treated simultaneously, in contrast to previous compilations of Pitzer parameters. Prior to fitting, a critical assessment of the available information for each system was made using the JESS database and software. Employing linear regression with singular value decomposition and using an appropriate objective function criterion, more than two-thirds of the systems could be satisfactorily fitted to the upper concentration limit of the available data. Only six electrolytes proved to be completely intractable using the present Pitzer model. All of these systems (which included HF, H 2SO 4, and H 3PO 4) are known to exhibit significant changes in chemical speciation at low concentrations (even though ion association per se does not preclude a satisfactory fit). The present Pitzer ion-interaction parameters provide a coherent, up-to-date set of empirical coefficients that can be combined in a self-consistent manner to produce multicomponent electrolyte solution models having a minimum of computational uncertainty in bulk solution properties such as density, heat capacity, and water activity. © 2011 American Chemical Society.