A method of making a gas separation membrane by providing a plating vessel with a volume of plating solution of gas-selective metal ions into which is placed a porous support. The plating solution is circulated over a surface of the porous support while maintaining conditions within the plating vessel so as to promote the electroless deposition. The circulation rate of the plating solution is such as to enhance the metal deposition onto the surface of the porous support in the formation of the gas separation membrane.