FAR 91.211 tells us when supplemental oxygen is required, but it's not very specific as to how that oxygen is to be provided. FAR 23.1447 gives some information about installed systems, but I can't find much on FAA requirements if you're using a portable system (cylinder, regulator, and cannula/mask like a Mountain High system).

Are there specific requirements/recommendations regarding portable oxygen equipment for Part 91 General Aviation, or can you just pick up a a medical or welding tank, stick a regulator on it, and pass out masks to your passengers?