Intravenous oxygenation represents a potential support modality for patients with acute and other respiratory failures. Our group has been developing an intravenous oxygenator, the IMO, which uses a rapidly pulsating balloon to enhance gas exchange performance. The purpose of this study was to compare the gas exchange of our current IMO device to that reported for a previous intravascular oxygenator, the IVOX, which underwent human clinical testing. An ex-vivo mock vena cava flow loop was constructed which was equivalent to that used previously for testing of the IVOX. The flow loop was perfused directly from an anesthetized calf with inflow from the IVC and outflow to the right atrium. O2 and CO2 gas exchange were measured from 1 to 4 1/2 LPM blood flows and for balloon pulsation rates up to 180 bpm. The gas exchange levels of the IMO at maximal balloon pulsation, normalized for fiber surface area, were approximately 1.5 to 3 times that of the IVOX. A significant finding was that balloon pulsation in the IMO reduced some of the natural dependence of the gas transfer rate on blood flowrate. Thus, in clinical application the IMO may exhibit less gas transfer variability due to differences in cardiac output.