We present new measurements of the osmotic coefficients of the binary system H2O + NaCl for temperatures from 293.15 to 363.15 K and for salt molalities from 1 to 5.5 mol . kg(-1) of water. Osmotic coefficients were deduced from vapor pressure measurements using a new nonisothermal static apparatus which is also described. Our experimental results were fitted using Apelblat’s correlation and are in very good agreement with those presented in the literature, especially with reference to the data from Clarke.