Disclosed is a cylindrical, single-component two-stage regulator for controlling a pressure and a flow rate of a gas. The regulator includes a housing for holding the two stages having an ingress adapted for connection to a source of gas at a high input pressure and an egress adapted for supplying gas at a lower output pressure than the high input pressure; a first stage for reducing the pressure of the gas from the high input pressure to a fixed intermediate pressure; and a second stage for reducing the pressure of the gas from the fixed intermediate pressure to the lower output pressure and regulating the flow rate of the gas out of the egress. One application of the present invention is for use in SCUBA (Self-Contained Underwater Breathing Apparatus) applications, where it replaces the traditional two-component user-adjustable regulator. The regulator may be made out of stainless steel, and is small enough to fit into a user's mouthpiece.