Oxygen cylinders: Cylinders are steel or aluminium bottles that contain gaseous oxygen (GOX) at a pressure of 200 bar. A cylinder loses no oxygen and can therefore be kept long, unlike liquid oxygen (LOX) vessels which loose oxygen by e.g. movement. Cylinders come in many sizes, from 0.6 litres to 50 litres. In general are steel cylinders used in Europe and aluminium in the USA.