Abstract: A blood oxygenator having a housing with an outer walled portion and a top portion and bottom portion. Blood is introduced through the bottom portion of the housing to be oxygenated by a fiber bundle having blood and oxygen flow. A blood outlet manifold in the upper portion of the housing is connected to a blood outlet on one end having a conical passage. The blood outlet manifold includes a reservoir with an increasing volume toward the conical passage and is sloped upwardly to enhance gaseous microemboli disentrainment. The wall of the housing decreases in dimension upwardly toward the blood outlet manifold, while the introduction of blood to the fibers is in a lesser ratio to the area adjacent the outlet manifold.