A gas recovery device utilizes membranes of a gas permeable, liquid impermeable substance to strip gas from gas-containing liquids, such as brine in subterranean geological formations. The device includes a shell defined by perforated outer walls and a plurality of elongated permeation tubes. Only one end of the tubes is attached to a plenum with the tube lumina in fluid communication with the plenum. The remainder of the tubes is not anchored and therefore is free to move. Substantially liquid-free gas is removed from the plenum through a pipe to a remote facility for storage and use. The gas recovery device can be deployed within the casing of a well suspended by the product discharge pipe and immersed in gas-containing brine flowing from a natural geological formation. The brine seeps into the well casing and flows through the perforations to surround the permeation tubes. Gas from brine in contact with the gas permeable membrane surface transports into the tube lumina, collects in the plenum and is displaced through the discharge pipe for use at a remote location. The movement of the free ends of the tubes provides agitation within the shell effective to disturb the boundary conditions at the surface of the membrane thereby promoting transport of gas through the membrane.