The BBC has spoken to Oisin Fanning, who has been on a deep sea voyage to the Titanic wreck before and knows a few of the people on board the missing submersible.
He said there is a lot of training beforehand. You wake up at 04:00 and safety procedures are ongoing for about four to five hours before it even descends into the water.
Fanning thinks those onboard would understand how to maximise their oxygen supply.
"They will immediately look to conserve oxygen straight away," he said.
"They will do everything to keep themselves calm, breathe shallowly and preserve the oxygen for as long as possible.
"I think they’ll last with oxygen for longer than people think."