OceanGate cofounder: Titanic sub passengers can survive past the time their oxygen is meant to run out

• The cofounder of the firm whose Titan submersible has gone missing remains hopeful for the crew.
• Guillermo Sohnlein said there was a "longer window" for rescue than many people think.

A founder of the company whose Titan submersible has gone missing in the North Atlantic broke his silence Thursday to say he remains hopeful for the rescue of its five-person missing crew, which includes his cofounder Stockton Rush.

Guillermo Sohnlein founded OceanGate with Rush in 2009 to offer private ocean exploration on manned submersibles. He remains a minority shareholder, but is no longer involved with the company. Rush, 61, who is OceanGate's CEO, is the submersible's pilot.

In a personal statement, Sohnlein said he last spoke to Rush a couple of weeks before the expedition's launch.

He said the missing crew could make their oxygen last longer by remaining calm.

"Today will be a critical day in this search and rescue mission, as the sub's life support supplies are starting to run low," Sohnlein said in his statement to Insider.

"I'm certain that Stockton and the rest of the crew realized days ago that the best thing they can do to ensure their rescue is to extend the limits of those supplies by relaxing as much as possible.

"I firmly believe that the time window available for their rescue is longer than what most people think. I continue to hold out hope for my friend and the rest of the crew."

The chances that the sub will be found with its crew still alive are slim. Rescuers have yet to give any indication that they know where the submersible is located.

Possible scenarios include a hull breach, fatal to the crew; that the Titan has surfaced with the passengers deadbolted inside; or that the Titan is in the deep sea, posing a mammoth rescue challenge.

The Titan was part of an expedition to take four tourists and Rush, as pilot, to the wreck of the Titanic, launching Sunday morning. It went missing an hour and forty-five minutes into its descent after losing communications with mothership Polar Prince, the US Coast Guard said Monday afternoon.

A search for the 21-foot sub began Monday and was still continuing Thursday, the Coast Guard said. Officials said Tuesday that the sub had around "40 hours of breathable air left."

"Banging" sounds were heard in the search area, around 400 miles from Newfoundland in Canada, on Tuesday and again on Wednesday, US Coast Guard officials said in a press conference Wednesday, but the source of these sounds remains unclear. At the time of publication, the sub is estimated to have only a few hours of oxygen left.

Stockton Rush was joined by passengers Hamish Harding, a British billionaire, French diver Paul-Henri Nargeolet, businessperson Shahzada Dawood and his 19-year-old son Suleman.

Experts have previously told Insider that the crew could extend the limit of their oxygen supplies by breathing shallowly and controlling their breath. They also say that estimated oxygen levels aren't necessarily indicative of how long the passengers can survive once supply runs out.

Read more: Everything we know about the Titanic sub

Read the full statement to Insider from OceanGate cofounder Guillermo Sohnlein:

"For the past three days, I have watched from afar as hundreds of dedicated professionals worked tirelessly to find and rescue the crew of the research submersible, Titan, with which communication was lost during its science expedition to the wreck of the Titanic. The pilot is my cofounder and friend, Stockton Rush.

"Today will be a critical day in this search and rescue mission, as the sub's life support supplies are starting to run low. I'm certain that Stockton and the rest of the crew realized days ago that the best thing they can do to ensure their rescue is to extend the limits of those supplies by relaxing as much as possible. I firmly believe that the time window available for their rescue is longer than what most people think.

"I would encourage everyone to remain hopeful for getting the crew back safely. In 1972, a similar rescue operation was able to retrieve two pilots trapped in a downed submersible with only 72 hours of life support. I continue to hold out hope for my friend and the rest of the crew.

"While I completely understand the public's interest in this situation and the media's need to cover it as a notable story, I ask that we wait until after the crew returns and conducts a proper debrief to speculate on what happened. We need to give those involved with the rescue enough room to focus on their work, and we need to give the crew's families privacy to deal with their emotions in their own personal way.

"For myself, I have been overwhelmed by the outpouring of support I have received from friends and colleagues all over the world. It has been impossible to respond, but please know that your messages are truly appreciated, so ... thank you!"