While oxygen cylinders are classified as “Dangerous items” in terms of air transportation, only medical oxygen cylinders are allowed to be transported by air.
For passengers who require oxygen therapy on board, there is a medical oxygen cylinder rental service available (charged). If you want to use a medical oxygen cylinder at an airport, please make your own arrangements to do so.
Passengers who require oxygen therapy on board are required to submit a medical certificate specified by the airline.
Check here for more details.