An oxygen mask is a mask that provides a method to transfer breathing oxygen gas from a storage tank to the lungs. Oxygen masks may cover only the nose and mouth (oral nasal mask) or the entire face (full-face mask). They may be made of plastic, silicone, or rubber. In certain circumstances, oxygen may be delivered via a nasal cannula instead of a mask.

Medical plastic oxygen masks are used primarily by medical care providers for oxygen therapy because they are disposable and so reduce cleaning costs and infection risks. Mask design can determine accuracy of oxygen delivered with many various medical situations requiring treatment with oxygen.

Oxygen is naturally occurring in room air at 21% and higher percentages are often essential in medical treatment. Oxygen in these higher percentages is classified as a drug with too much oxygen being potentially harmful to a patient's health, resulting in oxygen dependence over time, and in extreme circumstances patient blindness. For these reasons oxygen therapy is closely monitored. Masks are light in weight and attached using an elasticated headband or ear loops. They are transparent for allowing the face to be visible for patient assessment by healthcare providers, and reducing a sensation of claustrophobia experienced by some patients when wearing an oxygen mask. The vast majority of patients having an operation will at some stage wear an oxygen mask; they may alternatively wear a nasal cannula but oxygen delivered in this way is less accurate and restricted in concentration.

The global disposable oxygen masks market, according to Altus Market Research, has the potential to grow by US$1.1 billion between 2019 and 2023. The market's growth pace will also pick up speed throughout this time.

Silicone and rubber oxygen masks are heavier than plastic masks. They are designed to provide a good seal for long-duration use by aviators, medical research subjects, and hyperbaric chamber and other patients who require administration of pure oxygen, such as carbon monoxide poisoning and decompression sickness victims. Dr. Arthur H. Bulbulian pioneered the first modern viable oxygen mask, worn by World War II pilots and used by hospitals. Valves inside these tight-fitting masks control the flow of gases into and out of the masks, so that rebreathing of exhaled gas is minimised.

Hoses or tubing connect an oxygen mask to the oxygen supply. Hoses are larger in diameter than tubing and can allow greater oxygen flow. When a hose is used it may have a ribbed or corrugated design to allow bending of the hose while preventing twisting and cutting off the oxygen flow. The quantity of oxygen delivered from the storage tank to the oxygen mask is controlled by a valve called a regulator. Some types of oxygen masks have a breathing bag made of plastic or rubber attached to the mask or oxygen supply hose to store a supply of oxygen to allow deep breathing without waste of oxygen with use of simple fixed flow regulators.

An early 1919 high-altitude oxygen system used a vacuum flask of liquid oxygen to supply two people for one hour at 15,000 ft (4,600 m). The liquid passed through several warming stages before use, as expansion when it evaporated, and absorbed latent heat of vaporization, would make the gasified oxygen so cold that it could cause instant frostbite of the lungs.

The first successful creation for the oxygen mask was by Armenian born Dr. Arthur Bulbulian, in the field of facial prosthetics, in 1941.^{[citation needed]}