In the event of an influenza pandemic, patients with severe acute respiratory failure (ARF) due to influenza will require positive-pressure ventilation (PPV) in order to survive. In countries with widely available critical care services, PPV is delivered almost exclusively through use of full-feature mechanical ventilators in intensive care units (ICUs) or specialized hospital wards. But the supply of these ventilators is limited even during the normal course of hospital functioning. Purchasing and maintaining additional full-feature mechanical ventilators to be held in reserve and used only during mass casualty events is too expensive to allow the stockpiling of such equipment. Consequently, planning and preparedness efforts to respond to a severe influenza pandemic have stimulated consideration of limited-feature, less-expensive ventilation devices to augment traditional PPV capacity. This article offers guidance to authorities charged with preparing for mass casualty PPV in deciding which PPV equipment would be adequate for ventilating patients for days, weeks, or even months during a medical catastrophe.