Abstract: The present invention relates to an improved method and apparatus for dispersing a gas into a liquid. Gas is injected into a liquid and the flowing gas-liquid mixture is accelerated by a flow area contraction to at least sonic flow velocity, and subsequently decelerated by a flow area expansion to subsonic velocity. The attendant shock waves disperse the gas in the liquid. Preferred embodiments include off-centering the gas injection direction from the centerline of the contracting flow area and controlling the pressure at the exit of the expanding flow area.