Abstract: An oxygenator, particularly for proving oxygen and/or carbon dioxide or other gases to culture medium used in the in vitro culture of animal cells, comprised of a collection of elongate gas-permeable, liquid-impermeable tubes through which oxygen-containing gas flows and permeates through the tube walls to provide bubble- and foam-free oxygen gas to medium in contact with or in proximity to the tubes, the individual tubes having an outside diameter of less than about 1 mm and a wall thickness of from about 0.1 mm to about 0.25 mm, the tube collection preferably be radially spread apart at at least one point along its length.