In conditions of changed reserve structure of developed oil fields and increase of difficult to recovery oil part the special urgency is oil recovery by the tertiary thermal-gaseous methods based on process of displacement of residual oil by steam or hot water in a combination with carbon dioxide CO2. The main factor of the displacement mechanism with hot agents is thermal expansion of oil and viscosity decrease. In some cases hot water injection is more preferable in comparison with steam injection. Along with it recently has increased interest in so-called injection of "wet CO2", as combination of processes of thermal stimulation and solvents injection. Using CO2 as solvent in the combined technique is defined by its economic profitability, good solubility in high viscous oil promoting its "swelling", and also possibility of a reuse of gas after oil extraction. "Wet CO2" first of all provides warming up of layer, simultaneously being partially dissolved in oil. Besides this value of density of the oil saturated with carbon dioxide, and also dissolved in oil "wet CO2", become more than density of oil undersaturated with CO2. The laboratory researches show, that with dissolution in oil CO2 saturated by steam it is observed greater increase in its density, than under dissolution in it CO2 with smaller moisture content and this factor gets the special importance in the light of development of displacement mechanism. For an estimation of oil displacement efficiency from porous medium by steam and "wet CO2" a laboratory test on experimental installation has been carried out. Within the limits of the above described mechanism of combined injection of «wet CO2» the new technological decision based on an effective way of in-situ generation of "wet carbon dioxide" is offered. Saturation of generated CO2, reached by preliminary injection of gasforming and thermal agents (heat-transfer fringes — steam or hot water), provides necessary thermodynamic conditions and increases a sweep efficiency including reduction of fractals in displacement front. The technology of the method allows controlling speed and volume of generated gas, and thermobaric layer conditions and mineralization of a water basis of gas-yielding solutions — a phase state of CO2. Allocated carbon dioxide being dissolved in oil, along with viscosity change promotes density increase and, thus stimulates process of density segregation. Thus, the oil saturation on forward front of displacement increases that finally conducts to increase of oil recovery factor. From the point of view of a process efficiency increase, possibility of prevention and reduction of decrease in porous medium durability observed under hydrothermal treatment by change of pH indicator of injected agents is investigated. One of the ways to prevent montmorillonite formation is preliminary effect on the porous medium with water solution of hydrochloric acid. In the offered combined way of gas-thermal stimulation on a fields with heavy oil appropriate conditions are maintained using chemical agents participating in in-situ generation of carbon dioxide. The technological solution initially allows to prevent synthesis of new minerals — bulking up montmorillonite, and thus, to keep primary hardness of porous medium and permeability of productive collectors. It is reached by that consecutive alternate injection of hydrochloric acid water solutions and the gas-yielding agent along with forcing of the agent-heat-carrier, will reduce considerably both risk of formation of montmorillonite minerals, and reduction of hardness of porous media under bed stimulation. The technology is tested on oil fields of Russian Federation, USA, China and Azerbaijan.