Liquid oxygen, sometimes abbreviated as LOX or LOXygen, is a clear

cyan Cyan () is the color between blue and green on the visible spectrum of light. It is evoked by light with a predominant wavelength between 500 and 520 nm, between the wavelengths of green and blue. In the subtractive color system, or CMYK c ...

liquid Liquid is a state of matter with a definite volume but no fixed shape. Liquids adapt to the shape of their container and are nearly incompressible, maintaining their volume even under pressure. The density of a liquid is usually close to th ...

form of

dioxygen There are several known allotropes of oxygen. The most familiar is molecular oxygen (), present at significant levels in Earth's atmosphere and also known as dioxygen or triplet oxygen. Another is the highly reactive ozone (). Others are: * Ato ...

. It was used as the

oxidizer An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ''electron donor''). In ot ...

in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an application which is ongoing.

Physical properties

Liquid oxygen has a clear

color and is strongly

paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...

: it can be suspended between the poles of a powerful

horseshoe magnet A horseshoe magnet is either a permanent magnet or an electromagnet made in the shape of a horseshoe (in other words, in a U-shape). The permanent kind has become the most widely recognized symbol for magnets. It is usually depicted as red a ...

. Liquid oxygen has a density of , slightly denser than liquid water, and is

cryogenic In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th International Institute of Refrigeration's (IIR) International Congress of Refrigeration (held in Washington, DC in 1971) endorsed a univers ...

with a freezing point of and a boiling point of at . Liquid oxygen has an

expansion ratio The expansion ratio of a liquefied and cryogenic substance is the volume of a given amount of that substance in liquid form compared to the volume of the same amount of substance in gaseous form, at room temperature and normal atmospheric pressure ...

of 1:861 and because of this, it is used in some commercial and military aircraft as a transportable 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. Further, if soaked in liquid oxygen, some materials such as coal briquettes,

carbon black Carbon black (with subtypes acetylene black, channel black, furnace black, lamp black and thermal black) is a material produced by the incomplete combustion of coal tar, vegetable matter, or petroleum products, including fuel oil, fluid cataly ...

, etc., can

detonate Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves wit ...

unpredictably from sources of ignition such as flames, sparks or impact from light blows.

Petrochemical Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable s ...

s, including

asphalt Asphalt most often refers to: * Bitumen, also known as "liquid asphalt cement" or simply "asphalt", a viscous form of petroleum mainly used as a binder in asphalt concrete * Asphalt concrete, a mixture of bitumen with coarse and fine aggregates, u ...

, often exhibit this behavior. The tetraoxygen molecule (O₄) was predicted in 1924 by

Gilbert N. Lewis Gilbert Newton Lewis (October 23 or October 25, 1875 – March 23, 1946) was an American physical chemist and a dean of the college of chemistry at University of California, Berkeley. Lewis was best known for his discovery of the covalent bon ...

, who proposed it to explain why liquid oxygen defied Curie's law. Modern computer simulations indicate that, although there are no stable O₄ molecules in liquid oxygen, O₂ molecules do tend to associate in pairs with antiparallel

spins The spins (as in having "the spins") is an adverse reaction of Substance intoxication, intoxication that causes a state of vertigo and nausea, causing one to feel as if "spinning out of control", especially when lying down. It is most commonly as ...

, forming transient O₄ units.

Liquid nitrogen Liquid nitrogen (LN2) is nitrogen in a liquid state at cryogenics, low temperature. Liquid nitrogen has a boiling point of about . It is produced industrially by fractional distillation of liquid air. It is a colorless, mobile liquid whose vis ...

has a lower boiling point at −196 °C (77 K) than oxygen's −183 °C (90 K), and vessels containing liquid nitrogen can condense oxygen from air: when most of the nitrogen has evaporated from such a vessel, there is a risk that liquid oxygen remaining can react violently with organic material. Conversely, liquid nitrogen or

liquid air Liquid Air was the marque of an automobile planned by Liquid Air Power and Automobile Co. of Boston and New York City in 1899. page 1432 A factory location was acquired in Boston, Massachusetts in 1899 and Liquid Air claimed they would constr ...

can be oxygen-enriched by letting it stand in open air; atmospheric oxygen dissolves in it, while nitrogen evaporates preferentially. The

surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension (physics), tension is what allows objects with a higher density than water such as razor blades and insects (e.g. Ge ...

of liquid oxygen at its normal pressure boiling point is .

Uses

In commerce, liquid oxygen is classified as an

industrial gas Industrial gases are the gaseous materials that are Manufacturing, manufactured for use in Industrial sector, industry. The principal gases provided are nitrogen, oxygen, carbon dioxide, argon, hydrogen, helium and acetylene, although many other ...

and is widely used for industrial and medical purposes. Liquid oxygen is obtained from the

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

found naturally in

air An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

fractional distillation Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. It uses distillation ...

in a cryogenic air separation plant.

Air forces have long recognized the strategic importance of liquid oxygen, both as an oxidizer and as a supply of gaseous oxygen for breathing in hospitals and high-altitude aircraft flights. In 1985, the USAF started a program of building its own oxygen-generation facilities at all major consumption bases.

In rocket propellant

Liquid oxygen is the most common

liquid

propellant for spacecraft rocket applications, usually in combination with

liquid hydrogen Liquid hydrogen () is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecule, molecular H2 form. To exist as a liquid, H2 must be cooled below its critical point (thermodynamics), critical point of 33 Kelvins, ...

kerosene Kerosene, or paraffin, is a combustibility, combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in Aviation fuel, aviation as well as households. Its name derives from the Greek (''kērós'') meaning " ...

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

. Liquid oxygen was used in the first liquid fueled rocket. The

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

V-2 missile also used liquid oxygen under the name ''A-Stoff'' and ''Sauerstoff''. In the 1950s, during the

Cold War The Cold War was a period of global Geopolitics, geopolitical rivalry between the United States (US) and the Soviet Union (USSR) and their respective allies, the capitalist Western Bloc and communist Eastern Bloc, which lasted from 1947 unt ...

both the United States' Redstone and

Atlas An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets. Atlases have traditio ...

rockets, and the

Soviet The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...

R-7 Semyorka The R-7 Semyorka (, GRAU index: 8K71) was a Soviet Union, Soviet missile developed during the Cold War, and the world's first intercontinental ballistic missile. The R-7 made 28 launches between 1957 and 1961. A derivative, the R-7A Semyorka, R ...

used liquid oxygen. Later, in the 1960s and 1970s, the ascent stages of the Apollo Saturn rockets, and the Space Shuttle main engines used liquid oxygen. As of 2025, many active rockets use liquid oxygen: *

Chinese space program The space program of the People's Republic of China is about the activities in outer space conducted and directed by the China, People's Republic of China. The roots of the Chinese space program trace back to the 1950s, when, with the help ...

** CASC:

Long March 5 Long March 5 (LM-5; zh, s=长征五号 , p=Chángzhēng wǔ hào) or Changzheng 5 (CZ-5), also known by its nickname "''Pang-Wu''" (胖五, "''Fat-Five''"), is a Chinese heavy-lift launch vehicle developed by the China Academy of Launch Vehicl ...

, Long March 6, Long March 7, Long March 8, Long March 12, ''

Long March 9 Long March 9 (, LM-9 or Changzheng 9, CZ-9) is a Chinese Super heavy-lift launch vehicle, super-heavy carrier rocket that is currently under development. It is the ninth iteration of the Long March (rocket family), Long March rocket family, named ...

'' ''(under development)'', ''

Long March 10 Long March 10 (), also known as the “''Next Generation crewed launch vehicle''” (), and previously and unofficially as the “''921 rocket''” () or the "''Long March 5G''" (a development of the Long March 5), is a Chinese Super heavy-lift l ...

'' ''(under development)'' ** Deep Blue Aerospace: ''Nebula-1'' ''(under development)'' ** Galactic Energy: '' Pallas-1'' ''(under development)'' ** i-Space: '' Hyperbola-3'' ''(under development)'' ** LandSpace: Zhuque-2E, '' Zhuque-3'' ''(under development)'' ** Orienspace: ''Gravity-2'' ''(under development)'' ** Space Pioneer: Tianlong-2, '' Tianlong-3'' ''(under development)'' * Europe **

European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...

Ariane 6 Ariane 6 is a European expendable launch system developed for the European Space Agency (ESA) and manufactured by a consortium of European companies, led by the prime contractor ArianeGroup. As part of the Ariane rocket family, it is operate ...

** Isar Aerospace: ''Spectrum'' ''(under development)'' ** Rocket Factory Augsburg: '' RFA One'' ''(under development)'' *

Indian Space Research Organisation The Indian Space Research Organisation (ISRO ) is India's national List of government space agencies, space agency, headquartered in Bengaluru, Karnataka. It serves as the principal research and development arm of the Department of Space (DoS), ...

: GSLV,

LVM3 The Launch Vehicle Mark-3 or LVM3 (previously referred as the Geosynchronous Satellite Launch Vehicle Mark III or GSLV Mk III) is a Multistage rocket, three-stage medium-lift launch vehicle developed by the ISRO, Indian Space Research Organisati ...

JAXA The is the Japanese national air and space agency. Through the merger of three previously independent organizations, JAXA was formed on 1 October 2003. JAXA is responsible for research, technology development and launch of satellites into o ...

(Japan):

H-IIA H-IIA (H-2A) is an active expendable launch system operated by Mitsubishi Heavy Industries (MHI) for the Japan Aerospace Exploration Agency. These liquid fuel rockets have been used to launch satellites into geostationary orbit; lunar orbi ...

, H3 *

Korea Aerospace Research Institute The Korea Aerospace Research Institute (KARI; ), established in 1989, is the aeronautics and space agency of South Korea. Its main laboratories are located in Daejeon, in the Daedeok Science Town. KARI's vision is to continue building upon in ...

Nuri Nuri is a place in modern Sudan on the west side of the Nile River, Nile, near the Fourth Cataract. Nuri is situated about 15 km north of Sanam, Sudan, Sanam, and 10 km from Jebel Barkal. History Nuri is the second of three Napatan bur ...

Roscosmos The State Corporation for Space Activities "Roscosmos", commonly known simply as Roscosmos (), is a State corporation (Russia), state corporation of the Russian Federation responsible for space science, space flights, List of space agencies, c ...

(Russia):

Soyuz-2 Soyuz2 (; GRAU index: 14A14) is a Russian expendable medium-lift launch vehicle and the seventh major iteration of the Soyuz rocket family. Compared to its predecessors, Soyuz-2 features significant upgrades, including improved engines and ...

, Angara * United States **

Blue Origin Blue Origin Enterprises, L.P. is an American space technology company headquartered in Kent, Washington. The company operates the suborbital New Shepard rocket and the heavy-lift New Glenn rocket. In addition to producing engines for its own ...

New Shepard New Shepard is a Reusable launch vehicle, fully reusable Sub-orbital spaceflight, sub-orbital launch vehicle developed for space tourism by Blue Origin. The vehicle is named after Alan Shepard, who became the List of space travelers by nationali ...

New Glenn New Glenn is a heavy-lift launch vehicle developed and operated by the American company Blue Origin. The rocket is designed to have a Reusable launch vehicle, partially reusable, two-stage design with a diameter of . The first stage is powered ...

** Firefly Aerospace: Firefly Alpha **

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

Space Launch System The Space Launch System (SLS) is an American Super heavy-lift launch vehicle, super heavy-lift Expendable launch system, expendable launch vehicle used by NASA. As the primary launch vehicle of the Artemis program, Artemis Moon landing progra ...

Northrop Grumman Northrop Grumman Corporation is an American multinational Aerospace manufacturer, aerospace and Arms industry, defense company. With 97,000 employees and an annual revenue in excess of $40 billion, it is one of the world's largest Arms industry ...

: '' Antares 300'' ''(under development)'' **

Rocket Lab Rocket Lab Corporation is a Public company, publicly traded aerospace manufacturer and List of launch service providers, launch service provider. Its Rocket Lab Electron, Electron orbital rocket launches Small satellite, small satellites, and ha ...

Electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

, ''Neutron'' ''(under development)'' **

SpaceX Space Exploration Technologies Corp., commonly referred to as SpaceX, is an America, American space technology company headquartered at the SpaceX Starbase, Starbase development site in Starbase, Texas. Since its founding in 2002, the compa ...

Falcon 9 Falcon 9 is a Reusable launch system#Partial reusable launch systems, partially reusable, two-stage-to-orbit, medium-lift launch vehicle designed and manufactured in the United States by SpaceX. The first Falcon 9 launch was on June 4, 2010, an ...

Falcon Heavy Falcon Heavy is a super heavy-lift launch vehicle with partial reusability that can carry cargo into Earth orbit and beyond. It is designed, manufactured and launched by American aerospace company SpaceX. The rocket consists of a center core ...

Starship A starship, starcraft, or interstellar spacecraft is a theoretical spacecraft designed for interstellar travel, traveling between planetary systems. The term is mostly found in science fiction. Reference to a "star-ship" appears as early as 1 ...

** Stoke Space: ''Nova'' ''(under development)'' ** United Launch Alliance:

Atlas V Atlas V is an expendable launch system and the fifth major version in the Atlas (rocket family), Atlas launch vehicle family. It was developed by Lockheed Martin and has been operated by United Launch Alliance (ULA) since 2006. Primarily used to ...

, Vulcan

History

*By 1845,

Michael Faraday Michael Faraday (; 22 September 1791 – 25 August 1867) was an English chemist and physicist who contributed to the study of electrochemistry and electromagnetism. His main discoveries include the principles underlying electromagnetic inducti ...

had managed to liquefy most gases then known to exist. Six gases, however, resisted every attempt at liquefaction and were known at the time as " permanent gases". They were oxygen,

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

, and

nitric oxide Nitric oxide (nitrogen oxide, nitrogen monooxide, or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes den ...

. *In 1877, Louis Paul Cailletet in France and Raoul Pictet in Switzerland succeeded in producing the first droplets of liquid air. *In 1883, Polish professors Zygmunt Wróblewski and Karol Olszewski produced the first measurable quantity of liquid oxygen.

Physical properties

Uses

In rocket propellant

History

See also

References

Further reading