...spiny is entirely right that O2 suppliers must follow the script, BUT, it's important to note that YOU don't have to. get the script (hardest part) then crank that regulator (you bought your own on amazon to save on leasing, right?) to whatever works....key being reservoir bag full enough for full breath each time. for many that's 15-25+ lpm...some even higher. no one knows or cares what that is, find the flow that works for you. some find that starting high then lowering as the hit subsides an effective strategy and saves O2.....
...one of the saddest phrases in clusterville is "oxygen doesn't work for me"...when, in fact, it doesn't work at that pathetic flow....turn that baby up!! and experiment with various breathing techniques too. hyperventilation most frequently reported successful, but also slow breathe and breathe and hold...or a combo of all, can be the bliss.....