A new method for the fabrication of supported nanoporous carbon membranes, involving ultrasonic deposition of the polymer precursor, is presented here. The method has been used to produce mechanically robust, continuous films of nanoporous carbon on tubular, macroporous stainless steel supports using polyfurfuryl alcohol as the polymer precursor. The films, which were characterized using microscopy and spectrometry, show unprecedented molecular sieving selectivities for very small molecules, such as oxygen, nitrogen, helium, and hydrogen.