Just because you need to travel with medical oxygen, this need not restrict the opportunities to travel overseas it just takes a little bit more planning. Flying with a Disability offers you the following advice to ensure a safe, happy flight. 
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Travellers who require oxygen for medical use are, unfortunately, subject to a charge per bottle. This rate varies between airline, and can be quite expensive. You will need to contact the airline at least 48hrs prior to flying to advise the flow rate, and to get full medical clearance, though this tends to be minor technicality. 
Charges for portable medical oxygen can vary greatly, usually between £30 and £100 ($50 – $150). It is interesting to note that many airlines charge not per canister, but per leg of your trip. So in a flight which involves two legs, you’re going to be charge twice as much a direct flight, despite the fact that you may be covering the same distance in the same length of time. 
Economically, therefore, it can work out a lot cheaper if you can organise a direct flight, though this may not always be possible.
If you need help with planning your trip use specialised medical oxygen companies who can help answer all your queries and make your journey stress-free and a safe landing.
There is also some planning whilst safely on the ground with back up services available for portable oxygen concentrators whilst travelling overseas so you can ensure to have a great holiday with medical oxygen.