When James Cameron talks, people listen.

Who else could open an R-rated independent Australian film with unknown actors in 2,787 domestic theaters — many of them IMAX venues?

Over the pic’s debut frame on Super Bowl weekend — not the ideal time to release a male-skewing movie — “Sanctum” grossed nearly $10 million in the U.S. and another $3 million in the U.K. and Oz.

Cameron was exec producer on the 3D underwater adventure and his name topped the credits. He developed it with Aussie author-explorer Andrew Wight, his collaborator on various aquatic ventures. Wight based the script, written with John Garvin, on his own near-death experience during a diving expedition into a labyrinth of underwater caves.

“It’s unique for the biggest filmmaker in world to put his time and name into an independent movie,” said Ben Browning, whose Wayfare Entertainment put up the pic’s $30 million production budget while selling distribution rights to Universal and Relativity Media.

Helmed by Alister Grierson, “Sanctum” was shot over 60 days starting in November 2009 in Queensland, Australia — partly on location but mostly on the soundstages and inside the large water tank at the Warner Roadshow Studios near Brisbane.

The film follows a group of cave explorers trapped deep underground when floodwaters from a tropical storm block their exit. Suspense centers on who — if anyone — will survive.

Although his real-life predicament wasn’t as dire as the story depicted onscreen, Browning didn’t anticipate some of the challenges his crew and actors would face.

“We thought we had the perfect production plan,” he said, “but we stacked the odds against ourselves. It’s not easy to put those 3D cameras under water, nor to have actors do all their own stunts. They had to learn to climb and dive.”

The filmmakers used the same PACE 3D rigs deployed on Cameron’s “Avatar,” equipped with Sony F950 digital cameras — except that they had to be encased in waterproof housings.

“Underwater 3D looks terrific and the bubbles give you a real sense of immersion,” said Browning, “but it’s a big hassle. The cameras are enormous and expensive, and there are 10 people floating around for each actor you see.”

“Sanctum” used two d.p.’s. Jules O’Loughlin, credited as director of photography, worked on the “dry” sequences as well as on underwater portions. Simon Christides, a director with Queensland production shingle Big Boy Films, is credited as underwater cinematographer. (Earlier accounts listed Christides as underwater operator, but now all parties seem to agree on his cinematographer status.)

“Sanctum” isn’t the first film to have two cinematography credits. To ensure he could meet a tight shooting schedule, Danny Boyle hired two d.p,’s for “127 Hours”; they worked simultaneously on two main units.

Browning enjoys the creative freedom of working outside the studio system. “You’re able to use bad language, kill off major characters at an unexpected point and do things that keep audiences on their toes,” he said. “You probably wouldn’t be able to pull that off if it were made under studio conditions.”

Bookings & Signings

Montana Artists has signed line producer Bob Williams (“Fringe”) and line producers/UPM’s Bonnie Weis (“Rizzoli & Isles”), Christopher Griffin (“Rizzoli & Isles”) and Chip Vucelich “Without a Trace”); d.p.’s Kenneth Zunder (“The Starter Wife”), Lloyd Ahern (“Army Wives”), Felix Monti (The Secret in their Eyes”); production designers Bernardo Trujillo (“Mao’s Last Dancer”), David Blass (“Justified”) and Eloise Stammejohn (“Commander in Chief”); costume designers Christine Bieselin Clark (“Tron: Legacy”) and Bina Daigeler (“Biutiful”); editor Richard Comeau (“La Cite”); and 2nd unit director/stunt coordinator Mike Smith (“Stepfather”).

Montana has booked UPM’s Cecilia Roque on HBO’s “How to Make it in America,” D.J. Carson on Guillermo Del Toro’s “At the Mountain of Madness” and Jan Foster on Christopher Nolan’s “The Dark Knight Rises”; and line producers Tracey Jeffrey on Disney Channel movie “Geek Charming,” Robert Ortiz on Simon West’s “Medallion,” Darren Demetre on Tim and Eric’s “Billion Dollar Movie,” Kathy Gilroy-Sereda on an untitled Lifetime project directed by Tim Busfield and Bob Williams on Fox pilot “Exit Strategy.”

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