The main difference is the amount of oxygen the two machines can deliver per minute. If an oxygen concentrator is labeled as a 5-liter model, it can deliver between 2 to 5 liters of oxygen per minute. If it is a 10-liter model, it can deliver anywhere from 2 to 10 liters of oxygen per minute. For reference, the average lung capacity of a healthy adult male is about 6 liters.15 If someone needs high-volume or high-pressure oxygen therapy, their doctor may prescribe a 10-liter oxygen concentrator instead of a 5-liter machine.