Aztec Kid is on the mark.
An actual event from a few years back showed what Aztec Kid posted is 100% correct. The crew diverted to LPLA with smoke in the cabin and landed with a nearly depleted pilot oxygen system (they fixed the problem before landing). When their story started to spead, we began to ask a lot of questions. There was simply not as much available time on 100% O2 as we thought.
Our minimum for ETOPS went from 1000 to 1100psi, and we notice that we are normally around 1600 now...thank to the crew´s statements.