Kathryn, There is a smaller portable tank . Last winter I had to be on oxygen for about 6 weeks, and I had a tank cylinder that was about 18 inches that was carried over the shoulder, but later I was suppose to get a smaller one that I would refill at home , it was flatter , looked more like a plastic box. I ended up not needing it, so can't give you as lot of details, I just know it would have been a lot easier to take when going out.