Determination of gas solubility in polar liquids was analyzed by applying the equations of state and mixing rules. The modified Nakamura-Bredveld-Prausnitz equation with classic mixing rules has been proposed. It was stated that description of gas solubility by MNBP equation needs temperature dependence of the interaction coefficient k(ij). The parameters of this dependence have been determined for some substances. The comparative calculations showed that the method of equations of state gives good description of CO2 solubility in water.