I am a high volume 02 user from 5L to 8L. I (62 years old) still work full time but my office looks more like a hospital room than a normal office. I had to set-up special racks in my vehicle so I can carry 12 e-tanks. I use a concentrator at home and a concentrator at work and oxygen bottles the rest. I can go through from 3 to 8 bottles in a day. I am still active (as possible) at church. I also use a medical scooter to get around. I am told by my oxygen supplier that I am their only high volume user that is still active. Are there more high volume users moving around out there?