Previous intravenous oxygenators relied on 02 diffusion to treat Acute Respiratory Distress Syndrome. However, bubble oxygenators may increase 02 transfer. Polypropylene and polysulfone hollow fiber membranes were modified using vapor graft polymerization (VGP) and solution graft polymerization (SGP) to decrease the pore size and porosity and increase the hydrophilicity of the fibers so that as 02 flowed through the treated fibers submerged in water the bubbles formed from the treated fiber would be smaller than those from pure fibers. Both methods increased the surface hydrophilicity; however, SGP decreased the fibers' porosity and pore sizes the most. After optimized VGP, 48% of polypropylene fibers' bubbles were 25-50 pm in radius, compared with 12% from pure polypropylene fibers. After optimized SGP, 38% of polysulfone fibers' bubbles were 25-50 pm in radius, compared with 21% from pure polysulfone fibers. However, treated polypropylene fibers required a pressure of 60 psig 02 to form bubbles.