The methods employed in determination of vapor pressures of liquids have been reviewed. The gas saturation method has been used to determine the partial and total vapor pressures of water-methanol solutions at 0°C. From the vapor pressure data thus obtained, activities and activity coefficients of water and methanol have been calculated and the results have been plotted against the mole fraction composition. The data obtained showed a positive deviation from Raoult' s law for the solution. The activity coefficient curves have been analyzed and found to satisfy the requirements of the Duhem-Margules equation. These curves have also been fitted with an empirical equation which has made possible extrapolation of the curves to infinite dilution. A discrepancy between the data obtained and the data for higher temperatures has also been discussed.