Liqui oxygen (also LOx, LOX or Lox in the aerospace, submarine and gas industry) is a form of the element oxygen. It has a pale blue color and is strongly paramagnetic. Liquid oxygen has a density of 1.141 g/cm³ (1.141 kg/L) and is moderately cryogenic (freezing point: 50.5 K (−222.65 °C), boiling point: 90.188 K (−182.96 °C) at 101.325 kPa (760 mm Hg). In commerce, liquid oxygen is classified as an industrial gas and is widely used for industrial and medical purposes. Liquid oxygen is obtained from the oxygen found naturally in air by fractional distillation. Liquid oxygen has an expansion ratio of 860:1 at 20 °C; and because of this, it is used in some commercial and military aircraft as a source of breathing oxygen.