The purpose of the work is to show how to employ the experimental data from geocryology and soil physics for thermodynamic calculations of gas hydrate phase equilibria by taking into account pore water behavior in sediments. In fact, thermodynamic calculation is used here to determine the amount of non-clathrated pore water content in sediments in equilibrium with gas and hydrate phases. A thermodynamic model for pore water behavior in sediments is developed. Taking into account the experimental water potential data, the model calculations show good agreement with the experimentally measured unfrozen water content for different pressure and temperature conditions. The proposed thermodynamic model is applied for calculations of three-phase equilibria: multicomponent gas phase (methane, natural gas, etc.) – pore water in clay, sand, loamy sand, etc. – bulk (or pore) hydrate. As a result, correlations have been established between unfrozen and non-clathrated water content in natural sediments.