The permeation of several different permanent gases through plasma polymer membranes was studied. The plasma polymers were produced by a microwave discharge of various fluorine-containing monomers. Plasma polymers made from fluorine-rich monomers (F/C approximate to 1) yield films with the highest selectivities; those made from low fluorine content monomers show very little selectivity among the various gases. CO2 solubility is very high in the fluorine-rich plasma polymers and gives rise to large CO2 to CH4 selectivities.