With only a week to go before the Oscars, the all-important Best Picture prize appears locked in a two-horse race between dark comedy "Birdman" and coming-of-age drama "Boyhood."

But as Hollywood counts down the days to next Sunday's show, some are suggesting that controversial blockbuster "American Sniper" could yet surprise, and beat the two indie films.

"'Boyhood' and 'Birdman' are the frontrunners, and 'American Sniper' is the dark horse," Matthew Belloni, executive editor of industry journal The Hollywood Reporter, told AFP.

"I wouldn't be surprised if 'American Sniper' had a last-minute surge, because of how well it's doing at the box office," he added, referring to the movie's $365 million-plus global box office haul so far.

The Academy Awards have traditionally favored more independent, art-house fare for Best Picture, handed out at the climax of Hollywood's annual December-to-February awards season.

Washed-up superhero star

"Birdman" -- about a washed-up superhero film star battling to revive his career on the stage -- is definitely more along its usual lines, as is "Boyhood," which took 12 years to make as the actors aged in real time.

Both have fared well in pre-Oscars shows, with "Boyhood" taking the Golden Globes' best film, while "Birdman' won a string of awards including top prizes at the Screen Actors Guild and Directors Guild of America.

But Clint Eastwood's "American Sniper" has unexpectedly stirred up the race, grabbing headlines both for its massive box office success and a row over its portrayal an Iraq war warrior.

Filmmaker Michael Moore claimed it hero-worships former Navy SEAL Chris Kyle, while Tea Party firebrand and former vice-presidential nominee Sarah Palin said leftists were "not fit to shine Chris Kyle's combat boots."

The question is, how many of the 6,000-odd voting members of the prestigious Academy of Motion Picture Arts and Sciences, the industry's elite body, will be swayed at this late stage?

They began casting ballots on February 6, and voting closes on Tuesday at 5:00 pm (0100 GMT Monday) -- after which only two PriceWaterhouse Coopers staff will know the results before the envelopes are opened on stage next Sunday.

While the Best Picture race is too close to call, several of the other key categories are seen as much easier to predict.

Julianne Moore is almost universally expected to win best actress for playing a professor suffering from early-onset Alzheimer's Disease in "Still Alice."

Patricia Arquette is the favorite for best supporting actress as the mother in "Boyhood."

Best actor is between "Birdman" star Michael Keaton and Britain's Eddie Redmayne as astrophysicist Stephen Hawking in "The Theory of Everything," while J.K. Simmons is tipped for supporting actor for jazz drama "Whiplash."

Belloni said his personal forecast for best director is Mexico's Alejandro Inarritu for "Birdman" -- with the best picture going to "Boyhood."

"So the Academy will split... much like it did last year," he said, referring to "12 Years a Slave" taking the best film prize in 2014, while "Gravity" helmer Alfonso Cuaron -- also Mexican -- took best director.

Uproar over all-white nominees

Talking of "12 Years a Slave," there was uproar last month when Oscar nominations were announced, over the fact that every single one of the 20 acting nominees are white.

While Martin Luther King Jr movie "Selma" is among the eight Best Picture nominees, eyebrows were raised that neither its British star David Oyelowo nor director Ava DuVernay were shortlisted individually.

"The real snub here is that David Oyelowo... I think a lot of people were surprised that he did not get a nomination for that," said Belloni.

More broadly, he said, Academy members "feel bad" that only white actors were nominated this year, but added: "I think the problem goes deeper than that.

"The Academy nominates the films that are put up for contention, and other than 'Selma' there really weren't films that featured minority actors in leading and hefty roles," Belloni added.

"It goes to the kinds of movies that are getting green-lit in Hollywood, and the kinds of people who are making those decisions. Hollywood has made strides in recent years to rectify the diversity problem, but it still exists."