Abstract: A stream of primarily water is treated to remove oxygen before injecting the water into an underground hydrocarbon reservoir. The pressure of water moving through a conduit (12) is reduced to a low level to maximize the dissolution of oxygen and other gases that are dissolved in the water. The resulting two phase mixture is separated by centrifugal action caused by rotating the water inside the conduit. The rotation is induced by flowing the water past fixed spin blades (20). The oxygen and any other gases are removed from the center of the conduit through a gas pipe (30) and eventually pass out of the system to the atmosphere via a vacuum pump (50). As an enhancement, nitrogen may be introduced upstream of the centrifuge.