Densities for two ternary systems, NaNO3 (1) + NaCl (2) + H2O (3) and NaNO3 (1) + KCl (2) + H2O (3), have been measured at (20, 25, and 30)degrees C. The experimental study was carried out for four total ionic strength values, I = I-1, + I-2 approximate to (0.1, 1, 2, and 3) mol.kg(-1), and for each total ionic strength, the values of the ionic strength fraction of the NaCl or KCl were y(2) approximate to 0.2, 0.4, 0.6, and 0.8. The parameters of the Pitzer model were fit to the experimental density values. Also, using this model, we determined the volume of mixing (Delta V-M) at constant ionic strength and at 25 degrees C, for the two ternary systems studied in the present work. In general, the values for Delta V-M are positive, which indicates that the mixed solutes possess an opposite structural form, resulting in an attraction with an increase in volume in every ternary system.