It's always in liters, more specifically L/min. I assume tank pressurization is standard across tank sizes and maybe internationally as well.For your average portable oxygen tank the flow rate will go up to about 6 L/min max, which is sufficient for most peoples' needs. In the hospital a standard wall O2 flow meter will get you to about 15 L/min max. For COVID pts we frequently have to go to high-flow O2, which maxes out around 50-60L/min; this method requires a hospital bed and a wall O2 outlet; a tank won't do at all. Sometimes we even supplement on top of that, e.g. Oxymask along with hi-flow. If they can't even keep up their O2 sats on hi-flow, we ship them off to the ICU and intubate them. Mortality rate at that point will increase to about 50/50.
Problem for Indians is that people who are sick enough from COVID to need hospitalization frequently cannot survive on just a regular oxygen tank's delivery capacity, as I said. Looks like from the reports almost everyone needing more than a simple O2 tank is straight up going to just die....