By Joan Faus and Horaci Garcia

LA MASSANA, Andorra (Reuters) -The daughter of French oceanographer Paul-Henri Nargeolet, one of five people inside a submersible missing near the Titanic wreck, said on Thursday she held hope they will be rescued but she is comforted by the knowledge that he is in the place he loved most.

Sidonie Nargeolet told Reuters she was living with "a lot of stress, very mixed emotions" as the search for the submersible in the depths of the Atlantic Ocean entered a critical phase, with air expected to run out for the five people aboard.

"I really hope they will find them and safe. I think we have to trust what they are doing and be confident," Nargeolet, 39, told Reuters in the town of La Massana, Andorra, where she lives.

Nargeolet said her 77-year-old father's vast experience with submarines made him "know how to react to problems" and she was confident he was able to manage the situation well.

"He is very passionate about the Titanic since they found it 30 years ago and I know now he is at the place he would like to be."

Her father's colleagues have described him as a leading expert on the Titanic with more than 35 dives to the wreck under his belt after a two-decade career in the French navy.

His daughter said she learned about the accident on Monday, when she received a text message from her father's spouse saying he should have been back at 6 p.m. on Sunday.

"I cried a lot," she said of her reaction to the news. She had last seen her father just before Christmas last year in Andorra.

"He sent me a message a week before (getting in the submersible) telling me the weather was bad, so they hadn't been able to go down, but that there was a great atmosphere," she said. "I sent him a message on Sunday for Father's Day but he didn't reply."

Nargeolet said her father had made his first trip to the wreck in 1987. On one trip in another vessel operated by U.S.-based OceanGate Expeditions, he told her that he was not sure he would return safely, although he eventually did.

"He knows how to handle a crisis situation. He is prepared for it. Here, I think that with the other people he would have explained to them, therefore, to breathe gently, so that we use less oxygen. And we also knows how to reassure them, that's very important. Maybe kick the submarine, so they can hear it," she said.

But she was realistic about time running out.

"What worries me is that they are not being found because there will be a moment in which they will run out of oxygen," Nargeolet said.

"Sometimes I don't check (the news) because I don't want to hear them saying that they now have very low oxygen. I prefer to listen to positive things, to hope, that they will continue looking for them," she said.

"If they are not found, it will be very sad for us because we will not see him again. What he liked the most was to be in a submarine, (near) the Titanic. He is where he really loved being. I would prefer him (dying) at a place where he is very happy," Nargeolet said, struggling to hold back her tears.

"So whether he's in a submarine and whether he's in the Titanic, I know he likes it. I hope there will be a good outcome, that they will find him. In any case … he is happy where he is … That's reassuring."

(Reporting by Joan Faus; Editing by Jon Boyle and Angus MacSwan)