I am at stage 3 and require a minimum of 6 lpm while at rest and as much as I can get walking. The yellow band tanks will last about 1 1/2 hours. Now here is my issue, with a full tank at home I leave and I go into a Dr office and by the time I get back home I have only 1/2 a tank left. Keeping in mind that I put the regulator on "conserve" when ever I am sitting down. Now what do I do with a 1/2 tank? 45 minutes is not a very long time. So I put a piece of tape on it saying its a 1/2 tank. Pretty soon I have several 1/2 tanks, not too crazy about going anyplace with them as I don't know how long they will really last..My solution is now I have a two wheeled cart that is made for 2 "C" label oxygen tanks. Now I can take 2... 1/2 full tanks or one full and 1... 1/2 full. ..I can get delayed in traffic and not have to worry or at the Dr office or where ever...