Whenrealityhurts: no civil airliner that I have ever heard of has had a passenger pressure feed O2 system which would be necessary above 30,000ft. Therefore an emergency descent is always required. Some carriers do indeed carry extra O2 supplies if their routes involve very high enroute MSAs and these will usually be in the low 20s or high teens. Not a situation that the original poster asked about. The only other situation that I have come across is the case with all freighter aircraft which may have depressurisation procedures at the mid twenties in order to fight on board fire.
I guess you already knew all this ? !..............