The storage capacity of depleted oil and gas reservoirs depends on numerous factors, such as volume, porosity, permeability, and reservoir temperature and pressure. Storage centres of carbon dioxide localised in depleted oil and gas reservoirs characterise a big porosity and volume of fissures. Porosity system is relevant for gas content and for gas flow behaviour in reservoir. Sequestration of carbon dioxide in deep reservoirs will be realised under supercritical conditions. Possibility formation of two-phase system: compressed gas and adsorbate is presented in this paper. The adsorbate density is similar to density of liquid. Supercritical gas in adsorbed state could be regarded as a sort of superheated liquid. The strong attraction to a surface causes adsorbed molecules to attain much higher density than that of a normal liquid. Under these conditions, adsorbed molecules are so compressed that they repel each other. The solubility of carbon dioxide in pure water and in aqueous NaCl solutions is relevant for carbon dioxide sequestration process. Because of its importance, many experimental studies have been carried on the solubility of CO2 in pure water and in aqueous NaCl solutions. The solubility of carbon dioxide increases with the increase of pressure and decreases with the increase of ionic strength. However, CO2 solubility varies irregularly with temperature. At medium pressures (<100 bar) CO2 solubility decreases gradually with temperature. At higher pressures (>100 bar), CO2 solubility decreases with temperature at first, and then it increases with temperature. The conditions of effective sequestration of carbon dioxide are discussed in the paper.