We use liquid oxygen, and have two tanks. kind of a pain sometimes, but Judi uses the "marathon" and can go around anywhere for about 7 hours on one fill up....heck, that's more than my Dodge !
We are looking into a concentrator....she had one before, and it's ok until you want to leave the rig for a trip to the store or wherever. There are other smaller portable units we are looking into, but the fact is they weigh in at around 15 lbs. average...that ain't portable to me.
The liquid comes from lincare, and they have facilities all over the country. Whatever you do, understand that the main reservoir when filled weighs a LOT....the lincare guy has always come to our rig to fill it, and has helped put it back into the closet.
Bill