Weight-average molecular weights and osmotic second virial coefficients obtained from lowangle laser-light-scattering (LALLS) measurements are reported for binary aqueous solutions of eight nonionic polymers at 25 °C. For dilute ternary aqueous solutions containing two polymers, cross osmotic second virial coefficients were also obtained from LALLS measurements. Using the truncated osmotic virial expansion, we find that the calculated water-vapor pressures for aqueous solutions of Dextran T-70 are in reasonable agreement with previously reported experimental vapor-pressure data in the dilute (<10 wt %) polymer region. At higher polymer concentrations, calculated vapor pressures are too low, indicating a need to include higher coefficients in the virial expansion.