The Intravenous Membrane Oxygentor (IMO) is a device that consists of hundreds of hollow fibers and an elastic, non-permeable, balloon that is positioned within the vena cava. The balloon inflates and deflates rhythmically to a given amplitude and frequency to generate cross flow, promote blood mixing, and enhance the gas exchange. The IMO has been designed to provide temporarily up to 50% of the O2 and CO2 exchange requirements to patients who suffer Acute Respiratory Distress Syndrome (ARDS) [1–4]. This illness affects approximately 150,000 people per year in the U.S. and is characterized by non-cardiogenic pulmonary edemas and a rapid and progressive malfunctioning of the lung . The IMO device is an alternative therapy to conventional treatments such as mechanical ventilation and extracorporeal membrane oxygenation [5–7]. This paper reports the investigation of the flow and oxygen transfer characteristics of the IMO device shown in Fig. 1(a) and describes the numerically obtained flow patterns and the oxygen transfer characteristics for stationary and pulsating balloon regimes.