Exchanged my empty oxygen cylinder for a full one and quickly noticed that the full cylinder is 5-6 inches shorter than the old. I was told it is the same cubic feet,that the wall thickness is thinner because of using high strength steel, and thus a smaller cylinder. The time before that I exchanged my empty for a full and noticed the cylinder was maybe a good 1/2 inch smaller,diameter wise. I was told the same thing,higher strength steel,thus smaller cylinder,but the same cubic feet. I don`t get it, why 2 different sizes,and yet the same amount of oxygen. I deal with Airgas,there is no one else anywhere near close by to deal with. I have a lease with them,and it`s for the large tank,which costs about 37 dollars. I really don`t like to deal with them but no other choice. And despite what I was told,I don`t believe Airgas. I wonder if it`s like everything else,smaller size ,same price.

Im in the gas bizz and that sound a bit like BS.  If you are that much shorter on the new cylinder, you will need to have pretty significantly higher pressure in the little cylinder to get to the SCF of the big cyl.  That being said, if the old big cyl was not an overpump (2640 psi) and was only done to 2400, and the new, small cylinder was an overpump, you might get close.  I think a tall oxygen is 337 SCF and the smaller one is 251 SCF, if they are at the same pressure.