NOVELTY - The method involves cooling gas stream (31), expanding cooled stream (31a) at intermediate pressure, and supplying expanded stream (31c) to a processing assembly (113). Collected distillation liquid stream is heated to strip out volatile components to discharge a bottom liquid product stream (37) i.e. predominantly liquid carbon dioxide. Distillation vapor stream obtained by condensing less volatile components from another distillation vapor stream is heated to supply a portion of the cooled stream and to discharge volatile residue gas fraction.    USE - Process for separating gas stream containing methane and carbon dioxide into volatile residue gas fraction, in a natural gas processing plant.    ADVANTAGE - The process enables regulating quantities and temperature of the feeds to the mass transfer unit in an effective manner, so as to maintain the temperature of the upper region of the mass transfer unit at specific temperature at which the major portion of carbon dioxide is recovered in the bottom liquid product. The process enables efficiently separating carbon dioxide from the hydrocarbon gas streams and reducing power requirements for compression, re-compression, pumping, external refrigeration, supplemental heating and tower reboiling. The process enables reducing the operating cost of the facility.    DETAILED DESCRIPTION - The third distillation vapor stream is collected from an upper region of the mass transfer unit and combined with vapor portion of the expanded cooled stream to form the latter distillation vapor stream. The latter distillation vapor stream is cooled for condensing the less volatile components and forming condensed stream and the former distillation vapor stream. An INDEPENDENT CLAIM is also included for an apparatus for separation of a gas stream containing methane and carbon dioxide into a volatile residue gas fraction.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a natural gas processing plant.    Gas stream (31)    Cooled stream (31a)    Expanded stream (31c)    Bottom liquid product stream (37)    Processing assembly (113)