helodriver87
Contributor
Sadly there are no US DOT (or TC) approved ali7s over here.
Us North Americans (US Canada & MX) basically get to choose from ali 30s, 40s, 63s, 80s and 100s.
63s sound good for O2 bottles until you realize they are the same diameter as 80s just shorter.
30s (if full) can make for good small O2 bottles in the ocean where you only have 45-60mins of deco anyway. 40s are semi-standard for most O2 purposes. 80s are reserved for "big" dives, usually really deep, long or both. Sometimes people use lp72s for O2 on cave dives as they are easy to get filled, heavy so you can puff up your drysuit, and you drop them at 20ft anyway.
I use an 80 for bigger dives where I'm expecting an hour+ of O2 time. For really big WKPP dives, 95s or the occasional 104 are typical for OC deco bailout O2, but that's a very narrow application.