Isopiestic measurements have been carried out at the temperature 298.15 K for two saturated aqueous solutions: {H2O + BaCl2(sat) + NaCl + NH4Cl} saturated with barium chloride and {H2O + BaCl2(sat) + mannitol(sat) + NaCl+ NH4Cl} saturated with barium chloride and mannitol. Taking sodium chloride (aq) as reference solutions, osmotic coefficients of the aqueous solutions were determined. The experimental results are well represented by the ideal-like solution model. (c) 2006 Elsevier Ltd. All rights reserved.