A co-founder of the company whose missing submersible is believed to have run out of oxygen remained hopeful for the five people aboard – saying he believes “the time window available for their rescue is longer than what most people think.”

Guillermo Söhnlein, who co-founded OceanGate Expeditions in 2009 with current CEO and Titan pilot Stockton Rush, struck an optimistic tone Thursday as the 96 hours of oxygen aboard the ill-fated vessel apparently ran out about 7:08 a.m.

“Today will be a critical day in this search and rescue mission, as the sub’s life support supplies are starting to run low,” he wrote in a statement on Facebook.

“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,” wrote Söhnlein, who left the company in 2013 but remains a minority shareholder.

“I firmly believe that the time window available for their rescue is longer than what most people think,” he continued, as the clock ticked inexorably toward the end of the available air supply.

Söhnlein encouraged people “to remain hopeful,” citing another incident more than 50 years ago.

“In 1972, a similar rescue operation was able to retrieve two pilots trapped in a downed submersible with only 72 hours of life support,” he wrote. “I continue to hold out hope for my friend and the rest of the crew.”

He also acknowledged the public’s fascination with the drama about the submersible, which was lost an hour and 45 minutes into its voyage to the iconic Titanic shipwreck 12,500 below the surface, but asked people for patience about the cause of the disappearance.

“I ask that we wait until after the crew returns and conducts a proper debrief to speculate on what happened,” Söhnlein said. “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.”

He noted that even though he is no longer involved with OceanGate other than as a minority equity owner, he has still kept in touch with Stockton, saying “the last time we spoke was a couple of weeks before this year’s Titanic expedition.”

OceanGate Expeditions told the Coast Guard late Sunday that the Titan was equipped with only 96 hours of oxygen.

In addition to Rush, French Titanic expert Paul-Henri Nargeolet, British billionaire Hamish Harding, and Pakistani businessman Shahzada Dawood and his 19-year-old son, Sulaiman, are onboard the Titan.

Their status remains unclear as US and Canadian officials work around the clock to rescue them.

On Thursday, US Coast Guard Rear Adm. John Mauger said search-and-rescue efforts would continue in full force despite the oxygen depletion.

“We use all available data and information to prosecute those searches, but we continue to find in particularly complex cases that people’s will to live really needs to be accounted for as well,” he said on NBC’s “Today” show without directly commenting about the air supplies.

“So we’re continuing to search and proceed with rescue efforts,” Mauger added.