Expired: Missing Titanic-bound Sub Runs Out of Oxygen — But Desperate Rescue for Five-man Crew Continues

There is still hope for a miracle amid fears the Titan Five's oxygen supplies have run out four days after their plunge to explore the most famous shipwreck in history, RadarOnline.com has learned.

L'Atalante arrived at the location at 7:48 ET and deployed Victor 6000, a deep-sea robot capable of reaching depths of 20,000 ft., which was set to arrive near Titanic's final resting place at 12,500 ft. below the surface of the North Atlantic ocean within two hours.

The Victor 6000 is equipped with arms that can cut cables and help move a stuck or stranded vessel by securing a cable onto the submersible — said to have a 96-hour oxygen supply — before it is hauled to the surface.

As an extensive search continues, many pray the five passengers could still be alive if they took all measures to conserve oxygen by sitting still, remaining calm, and sleeping.

One person can have their legs stretched out in the submersible while the others have to be cross-legged, based on a promotional picture released by OceanGate.

Three of the passengers are renowned adventurers including British billionaire Hamish Harding, OceanGate CEO Stockton Rush, and French navy veteran Paul-Henri Nargeolet.

Many speculate they would have taken necessary precautions to extend breathable air as long as possible if they are still stuck inside.

Also aboard is Pakistani businessman Shahzada Dawood and his 19-year-old son Suleman, who joined for the excursion which costs travelers $250,000 per-person.

The group set out Sunday and lost contact an hour and 45 minutes into their descent.

Despite a growing effort to save those onboard, the Titan has not yet been located and it is questioned if the vessel is stuck somewhere on the seabed at an angle which prevented it from rising to the surface.

There was banging heard at 30-minute intervals, multiple sources said, but it's unknown where the sound came from and if it could be the passengers trying to help rescuers find their location.

Retired U.S. Navy submariner Mark Martin questioned if the sub is being obstructed by view due to a big piece of debris from the decaying shipwreck, which is said to make noises. He said on WFLA News there could be a chance the Titan fell directly on top of Titanic and is entangled in the wreck, which may explain why the submersible has not yet been found.

Guillermo Sohnlein founded OceanGate with Rush in 2009 and speculated the timeframe to save the passengers could go beyond the US Coast Guard's prediction.

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"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 said amid concerns it may now be a recovery mission.

"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."