Group sex, violent sex, gay sex, and wife-swapping were among the central elements of stories in entries at the Cannes Film Festival this year.

Whether a reflection of changing sexual mores around the world or merely the work of edgy directors pushing new limits, Cannes audiences were shown a great number of films with stories revolving around or showing non-traditional sex.

"As the boundaries of what's considered acceptable on and off the screen get pushed back, directors are moving in to occupy that vacuum of space and push the boundaries even further," said Variety's European Editor Adam Dawtrey.

"In times that are tough for independent films, it's important for them to find an edge to give them some commercial appeal, though not in a cynical way. The instinct is: 'How do you grab audiences?' And the answer is with juicy scenes."

Films with heterosexual intercourse or romantic suggestions of it have long helped filmmakers in many genres to tell and sell their stories.

But this year a great diversity of sex has been displayed.

In "Where the Truth Lies", Kevin Bacon and Colin Firth play a popular entertainer duo with multiple daily sex partners, but their friendship ends after sex with their hotel maid goes awry.

"I wanted to create this world that was intoxicating," said Canadian director Atom Egoyan, describing the need for group sex. "They could take any amount of drugs they wanted and have as much sex as they wanted. It was an unbridled atmosphere."

"Don't Come Knocking" is about a degenerate Hollywood star played by Sam Shepard who learns he fathered two children, now adults, decades earlier. But he's slept with so many women in his life he at first can't even vaguely recall their mothers.

"Sam's character is a womaniser and that's one of his life's tragedies," director Wim Wenders told Reuters. "It's a disease like alcohol. It's why he missed his life because he was only always thinking of the thrill of sex, drugs and rock and roll."

In "Chromophobia", a prostitute played by Penelope Cruz wears a nurse's costume for a sex ritual with a client, an elderly retired judge who turns out to be her daughter's father.

In Woody Allen's "Match Point" a sizzling affair between the brother-in-law and sister-in-law in a rich British family starts in a rain-drenched wheat field but ends tragically after he gets her pregnant and kills her to keep the scandal romance a secret.

Wife-swapping is the spice in life belatedly discovered by a retired French couple in "Peindre ou Faire L'Amour".

Barry Pepper clips and smells his dirty toenails in "The Three Burials of Melquiades Estrada" before rising from the couch for a quick, animal-like sex session with his bored wife while she continues to watch television from the kitchen.

Perhaps the most controversial film is director Carlos Reygadas' "Batalla en el Cielo" (Battle in Heaven). It starts with a teen girl performing fellatio on an obese middle-aged Mexican who later has graphic sex with his even heavier wife.

But he rejected criticism sex in his film is gratuitous. "The whole world is involved in sex," Reygadas said.