Above is correct. Note opening the valve is not enough, you need to remove it so they can look inside. Takes the right tools. You can send it UPS ground.
Just check it and don't say anything. it will arrive and no one will care.
So these comments make me curious what do they do with folks who have medical oxygen on commercial flights - are they excluded from flying because of the bottle?
Greg
This! Ship it ahead (empty) and just do the fill.