How large? Can’t speak for the Mexicans but our Medevac, fixed wing and chopper, guys all use the small bottles, about 30 inches long and 5 inches in diameter. Storage pressure would typically be 1950 PSI. They use a different valve than industrial bottles but the Oxy is the same. Comes off the same manifold at the gas plant.
*** "...our Medevac, fixed wing and chopper, guys all use the small bottles, about 30 inches long and 5 inches in diameter. Storage pressure would typically be 1950 PSI. They use a different valve than industrial bottles but the Oxy is the same. Comes off the same manifold at the gas plant..."
~~~~~~~~~~~~~~~~~~~~~~~~~

Sounds like a "D" sized bottle. Our ambulances use them too.
🐷