Abstract: A blood oxygenator is equipped with a sparger having a passageway formed by two vertically aligned fluid impervious cones, one upright and one inverted, between the bases of which a porous disc is positioned. An oxygen inlet communicates with the porous disc to radially inject oxygen into the passageway from the periphery of the porous disc. The blood is transformed from a liquid to a foam as it rises in the passageway. At the outlet of the sparger an oxygenation chamber includes a serpentine cascade which prolongs contact between the blood and bubbles of gas containing oxygen. The outlet of the cascade empties into a reservoir which has a concave foam filter therein defining a defoaming chamber and a screen having uniform interstices surrounding the foam filter to form a bubble point barrier. The screen prevents undissolved gaseous emboli in the blood from passing from the defoaming chamber toward the arterial outlet of the reservoir.