Abstract: An apparatus and method for high pressure gas filling of gas cylinders is disclosed. The apparatus includes an elongated filling tube for a pressurized gas cylinder having a valve regulator/fitting sealed in an opening at one end of the gas cylinder, the elongated filling tube extending within the cylinder and being attached at one end to the valve regulator/fitting. The elongated filling tube is provided with longitudinally spaced transverse openings along the length thereof to facilitate intermixing of gases injected into the cylinder under pressure.