Oxygen tanks are used to store gas for:

• medical breathing at medical facilities and at home
• breathing at altitude in aviation, either in a decompression emergency, or constantly (as in unpressurized aircraft)
• oxygen first aid kits
• oxygen therapy
• gas blending, for creating diving breathing mixes such as nitrox, trimix and heliox
• open-circuit scuba sets – mainly used for accelerated decompression in technical diving
• some types of diving rebreather: oxygen rebreathers and fully closed circuit rebreathers
• use in climbing, “Bottled oxygen” refers to oxygen tanks for mountaineering
• industrial processes, including the manufacture of steel and monel
• oxyacetylene welding equipment, glass lampworking torches, and some gas cutting torches
• use as liquid rocket propellants for rocket engines
• athletes, specifically on American football sidelines, to expedite recovery after exertion.