Abstract: The method consists of recovering heat contained in the combustion gases in a first heat exchanger or boiler, recovering the heat given off by the engine or turbine in the form of steam and/or hot water, leading the previously cooled, in a second heat exchanger, combustion gases to a pressure gas holder, impelling the gases to a washing and cooling column and passing them through CO.sub.2 absorption columns wherein this latter is picked up whereas the remainder of gases, specially N.sub.2, are left free, and conventionally performing the steps for obtaining both gases. For performing all of the obtention procedure, use is made of only the combustion generated energy, thus thoroughly recovering the above gases with a whole benefit of the energy contributed by the hydrocarbons.