Oxygenator using porous hollow fiber membrane

An oxygenator comprising:

• a container having a blood inlet, a blood outlet, an oxygen-containing gas inlet and an oxygen-containing gas outlet;
• and
• a plurality of hydrophobic porous hollow fiber membranes, housed within said container, for defining therein passages for an oxygen-containing gas between said oxygen-containing gas inlet and said oxygen-containing gas outlet, and for defining a passage for blood outside said fiber membranes between said blood inlet and said blood outlet, said fiber membranes having an inside diameter of 150 to 300 .mu.m, a wall thickness of 10 to 150 .mu.m, and a substantially circular cross-section, an average crimp amplitude of 50 to 120% of the outside diameter thereof, a ratio of the maximum crimp amplitude to a crimp half cycle period at the maximum crimp amplitude in the range of 0.01 to 0.1, and a crimp ratio of 1.0 to 3.0%.