Abstract: A controlled volume buoyancy compensating device for providing the underwater control of buoyancy that is independent of changes in depth or dive position. The inventive device includes an adjustable air chamber, air source, and a demand regulator. The air chamber is a rigid shell with a volume adjustable by some means and sealed to keep water separate from air. The regulator is a two way demand regulator to provide or exhaust air at the ambient pressure and is essentially the same as a SCUBA diver's breathing regulator. The typical air source is a compressed air tank with pressure reducing valve to deliver air at about 140 psi above the ambient pressure.