Quote Originally Posted by MAC702 View Post
If I read your source correctly (thank you very much for citing one) that's an OSHA standard, not a DOT regulation. It would not be a requirement for those of us that are not under OSHA's jurisdiction. I'm not under OSHA, and it doesn't bother me at all to transport them flat when I see fit. My gas supplier doesn't even mention it when I load and unload cylinders for exchange, either.
Here in Houston I see lots of O2 cylinders being transported horizontally, both with and without regulators attached.