In spite of oxygen therapy, desaturations frequently occur during exercise in COPD patients. Although current recommendations are to add 1 L/min to the baseline oxygen flow during exertion, a new closed-loop system (FreeO2) automatically and continuously adjusts the oxygen flow to the patient's needs based on the oxygen saturation by pulse oximetry (SpO2), end-tidal CO2 (EtCO2) and respiratory rate. A preliminary study showed significant improvement in exercise tolerance in COPD patients not needing oxygen therapy. Although oxygen flow could be two fold increased during exercise, a worsening hypercapnia is plausible in severe COPD.