Extracorporeal blood oxygenators are used to oxygenate blood during open-heart surgery. Hydrophobic microporous flat-sheet or hollow-fiber membranes are used to separate blood and gas phases. Oxygen diffuses from the gas phase through the gas-filled membrane pores into the blood. Mass-transfer and friction-factor correlations have been developed for flat-sheet and hollow-fiber blood oxygenators. Generalized Graetz, Reynolds, and Schmidt numbers are used in these correlations to account for the shear-thinning behavior of blood. Because oxygen not only dissolves in plasma but also binds to hemoglobin, a mass-transfer enhancement factor based on film theory has been developed to account for oxygen binding to hemoglobin. Experimental results for oxygen transfer to bovine blood and both non-Newtonian and Newtonian blood analogue fluids indicate that the correlations developed may be used to predict the performance of a blood oxygenator based on results for an experimentally simple system such as the oxygenation of deionized water. (C) 2005 American Institute of Chemical Engineers.