Liquid oxygen has a pale blue color and is strongly paramagnetic. Liquid oxygen has an expansion ratio of 1:861 at 20 °C (68 °F); and because of this, it is used in some commercial and military aircraft as a source of breathing oxygen. Because of its cryogenic nature, liquid oxygen can cause the materials it touches to become extremely brittle. Liquid oxygen is also a very powerful oxidizing agent: organic materials will burn rapidly and energetically in liquid oxygen.
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 in a cryogenic air separation plant. Liquid oxygen is a common liquid oxidizer propellant for spacecraft rocket applications, usually in combination with liquid hydrogen or kerosene. Liquid oxygen is useful in this role because it creates a high specific impulse