At the risk of prompting another snide remark from abnfrog I will repeat what I mentioned previously. He took two bottles of O2 to the Doria but only used one. On return he filled the bottle that had been emptied and filled it with air for a trip to the caves. Unfortunately he took the other bottle of O2 that had not been used thinking it was the one with air. This is my understanding from what I have read.He's got a little bit of a point about air being a weird gas for the Doria. Crappy bottom gas and a crappy deco gas.
But it I still think o2 in a bottle marked o2 isn't a big surprise.
Maybe abnfrog could explain the purpose of that post, my post was an attempt at further clarification of Jim Lapenta's post.