Before my lung transplant I was on oxygen, 4L at rest and 8L with exercise or activity. For my trips to Mayo I had a Double Tank Cart so the tanks were more stable, and would stop to change tanks when needed. My oxygen supply company was very helpful with supplying me with the double tank cart and tanks. I had 10 large and 7 small tanks so I would not run out. I used their small tanks for quick in and out tasks.
Hope this helps,