"Every time I make a movie, everybody says it's the most expensive film in the industry," he says. All his films go over budget a little, but he admits that this was a different kettle of fish. "On Terminator 2, we had an $85 million budget that went to $95 million. True Lies went over about seven per cent. It's a lot of money, but as a percentage of the total and when you consider the scale of the project, it's not unreasonable.
"Titanic went over vastly more than that - 45 per cent. The question is, does that dissuade you from making the movie of your dreams? Does that dissuade you from making a movie like the movie that inspired you when you were a kid, that nobody else seems to be making? No." Ask what those inspirational movies were, and he names 2001: A Space Odyssey - "a wake-up call" - and Dr Zhivago. He cites Dr Zhivago and Gone With The Wind as inspirations for Titanic: big canvas, intimate story.
Much in Cameron's background suggests a macho man. Born in Canada, he was a machinist and truck driver and started in the film business as jackof-all-trades in the "guerilla film-making" school of Roger Corman - one reason, probably, why he doesn't fear frenzy. His "relaxations" include flying (T-38 jets), scuba-diving, and riding motorbikes with Arnold Schwarzenegger.
But the success of his films relies on the blend of action ("so adrenalised they just about dare the heart to keep beating" - US magazine) and emotion. Moreover, women have played a key role in Cameron's career. Gale Anne Hurd produced The Abyss for him when their divorce was going through. Kathryn Bigelow directed Strange Days from his script even after their marriage, too, had broken up. And his films have been notable for their strong female characters. "I like strong women, what can I say?"
Those same films have been described as "armour-plated comments on that ultimate battle, the one between the sexes". That's where we break with Titanic, actually. Stripped of the techno dress, it's an old-fashioned love story. "I like using hardcore technological means to explore an emotion." And exploring man's relationship with technology.
"The Titanic represented progress - the good side of technology - and people put their faith in it as we do in the silicon chip today. If all the silicon chips in the world exploded simultaneously, we'd be gnawing on each other's femurs in two weeks." He's said that before. He likes the image. He sees the "message" of Titanic as a caution, and talks about the haves and havenots on board. "If you were a male steerage-class passenger on the Titanic you stood a one-in-10 chance of survival. If you were a first class female, it was virtually 100 per cent."
His big film about a big subject was always going to be three hours long, though that could have been a problem commercially.
The film took $28 million in its opening weekend and even more than that on its second weekend in the charts. Many critics, too, were in ecstasy.
Even a success may not make all the participants happy in equal measure. While Fox are releasing Titanic internationally, Paramount have it for the US. But such newly fashionable distributing deals suddenly look less equitable in the light of Titanic's film history. Paramount put in a fixed sum - $65 million, plus $35 million in marketing costs - which they're almost bound to get back. Fox were left to pick up the rest of the costs as they spiralled, and had much more at risk. But they are clawing back their money aggressively. An American gift catalogue signed a deal with Fox to sell "artefacts" - $11,500 for an evening gown worn by Kate Winslet - from "perhaps the most historically accurate film ever made". That obsession with detail may just pay after all.
One Hollywood insider, quoted respectfully by US Premiere, estimates that in order to see a profit, Titanic will have to gross more than $500 million worldwide. But Men In Black took $527 million and Cameron's own Terminator 2 has made that much already.
Now, again, Cameron may have done something important for the Hollywood industry. "Modern studios exist to create people like Jim Cameron," Premiere wrote. "If they don't give him the money, they might as well just kill themselves." "I've never really been that concerned with where Hollywood thought I should be - otherwise I would never have made this film," says Cameron. "I think I've proved to my own satisfaction that I can do other things beside science-fiction techno-thrillers.
"I feel stronger as a film-maker as a result of Titanic." If the experiment goes badly, that will sound like egotism - $200 million for a learning experience? But if the film does well, it will just sound brave.
Titanic opens in Ireland on Friday.