Most of Los Angeles will be fast asleep when the nominees are revealed at a 5.30am (12.30am Wednesday, AEDT) ceremony, triggering the start of four frenzied weeks of studio campaigning ahead of Tinseltown's big night on February 25.

Until now, no single film has emerged as the favourite to dominate across multiple categories, even though clear front-runners have emerged for the top prizes - best picture, best director, best actor and actress.

"There are definite favourites for most of the marquee awards but ultimately I think you'll see the gold shared across several films," said Tom O'Neil, a columnist with the Los Angeles Times's theenvelope.com

In the best picture race, Golden Globes winner Babel, Martin Scorsese's gangster drama The Departed and the musical Dreamgirls head the field with The Queen and offbeat comedy Little Miss Sunshine making up the numbers.

However, analysts believe that there is still a chance Clint Eastwood's groundbreaking war drama Letters from Iwo Jima, shot entirely in Japanese, could enter the reckoning.

The critically acclaimed United 93, a fictionalised dramatization of the passenger uprising on one of the planes hijacked on September 11, 2001, is also seen as a possible outside bet.

In the best director category, Eastwood again could upset the form book. Scorsese, the overwhelming favourite to win this year's award having been passed over on five previous occasions, is likely to be the first name on most voters' ballots.

Babel director Alejandro Gonzalez Inarritu is also a certainty for a nomination, along with Bill Condon of Dreamgirls and Stephen Frears of The Queen.

Although the husband-and-wife team of Little Miss Sunshine, Jonathan Dayton and Valerie Faris, have been expected to make up the five nominees, analysts believe they could be bumped out by Eastwood.

The veteran actor-director is a perennial favourite with the Academy of Motion Picture Arts and Sciences's nearly 6000 voters, with two best director awards already, 1992's Unforgiven and Million Dollar Baby two years ago.

And his unique achievement in shooting two war films back-to-back, Flags of our Fathers and Letters From Iwo Jima, movies about the same battle viewed from American and Japanese perspectives, has won many admirers.

"I've talked to so many directors who tell me how impressed they are by Clint Eastwood's achievement doing two movies," said pundit Pete Hammond of hollwoodwiretap.com. "They're blown away by it."

In the best actress race, Oscar-watchers are unanimous about the likely line-up, with three British actresses expected to figure.

Leading the British contingent is Helen Mirren, fresh from a double victory at the Golden Globes, and a nomination lock for her portrayal of Queen Elizabeth II in The Queen.

Mirren is expected to be joined by compatriots Judi Dench, in Notes on a Scandal, and Kate Winslet, in Little Children.

While Mirren has been the front-runner for best actress for months, the claims of Meryl Streep for The Devil Wears Prada are gathering momentum. Streep - nominated an astonishing 13 times for an Oscar and a winner on two occasions - is seen as the biggest threat to Mirren's chances, with Spain's Penelope Cruz completing the quintet for Volver.

The best actor race is less clear-cut, with only two men viewed as certainties to earn a nomination.
Forest Whitaker is a safe bet for The Last King of Scotland, in which he plays Ugandan dictator Idi Amin. Veteran Irish actor Peter O'Toole is also a shoo-in to win his eighth Academy Awards nomination, for Venus, 45 years after his first, for Lawrence of Arabia.

But the remaining three best actor spots are up for grabs.

Leonardo DiCaprio's anguished performance as an undercover police officer in The Departed could earn him a nomination but speculation has mounted that he may have to settle for a place in the supporting actor category.

Other contenders are Ryan Gosling for Half Nelson, Ken Watanabe in Letters from Iwo Jima and, a long-shot, Sacha Baron Cohen for Borat.