An improved mixed matrix membrane for the separation of gases comprises a nitrogen containing compound such as an amine, silicone rubber and activated carbon on a porous support. The membrane may also comprise a carbonate such as potassium carbonate and a plasticizer such as polyethylene glycol. Membranes of this design may be used in processing natural gas or other gases. The gases which may be separated by the membrane include mixtures of methane and carbon dioxide, mixtures of oxygen and nitrogen, and mixtures of carbon dioxide and nitrogen.