Accurate prediction of the solubilities of air (as well as nitrogen: N2; oxygen: O2; and argon) in aqueous electrolyte solutions is very important for geological studies and in the chemical industry. However, very few electrolyte equations of state have been successfully used for the calculations of these gas solubilities. This work presents a thermodynamic modeling study on the solubilities of N2, O2, argon, and gas mixtures in pure water and aqueous solutions of several inorganic salts with the electrolyte Cubic Plus Association equation of state (e-CPA). The binary interaction parameters between the cation/anion and gas are obtained by fitting the experimental data of gas solubilities in single-salt solutions. The results show that the e-CPA can satisfactorily correlate the gas solubilities for most systems. For example, the e-CPA gives deviations of 4% for the O2 solubilities in aqueous NaCl solution. The e-CPA is then applied to predict the solubilities of gas mixtures and multisalt systems (gas mixture in pure water and gas mixture in aqueous multisalt solutions), and satisfactory performance is achieved. For example, the e-CPA gives deviations of 4% for the air solubilities in aqueous NaCl solution.