Talk show host Jimmy Kimmel was set to return for the fourth time to emcee the film industry's highest honors. The live broadcast on ABC starts at 4 p.m. PDT (2300 GMT), an hour earlier than usual.
As stars began arriving to walk the red carpet, hundreds of pro-Palestinian protesters angered by the Israel-Gaza conflict shouted and slowed traffic in the streets surrounding the Dolby Theatre in Hollywood. "While you're watching, bombs are dropping," one sign read.
"The Oscars are happening down the road while people are being murdered, killed, bombed," said 38-year-old business owner Zinab Nassrou.
At the awards venue, a handful of celebrities, including Eilish and her brother Finneas, were spotted wearing red pins calling for a ceasefire in Gaza.
"Oppenheimer," the three-hour drama directed by Christopher Nolan, led the field with 13 nominations. The movie was the frontrunner to win the prestigious best picture prize, capping its sweep of other major awards this year.
"If the best picture isn't 'Oppenheimer,' it will be one of the biggest upsets, if not the biggest upset, in the history of the Oscars," said Scott Feinberg, executive editor for awards at The Hollywood Reporter.
After 2023 was marred by actors and writers strikes, the Oscars give Hollywood a chance to celebrate two global hits. "Oppenheimer" and feminist doll adventure "Barbie," another best picture nominee, brought in a combined $2.4 billion in a summer box office battle dubbed "Barbenheimer."
"Barbie" star America Ferrera, a supporting actress nominee, sported a pink sequined dress on the Oscars red carpet. She said she was thrilled by "how the film was being enjoyed and loved" by moviegoers.
Oscar producers said they have planned unannounced cameos and other surprises to entertain audiences at home.
"My biggest hope is that they go through a range of emotions with us, that they feel happiness and joy, that we maybe make them shed a tear," Executive Producer Raj Kapoor said. "And then they somehow feel connected and inspired to also live their dreams."
Supporting actor nominee Ryan Gosling will sing the '80s-style rock anthem "I'm Just Ken" from "Barbie." Members of the Osage Nation will perform the nominated "Wahzhazhe (A Song for My People)" from "Killers of the Flower Moon."
Cillian Murphy, the Irish actor who played physicist J. Robert Oppenheimer as he led the race to build the first atomic bomb, is considered the favorite for best actor. Murphy's main competition, according to awards pundits, is "The Holdovers" star Paul Giamatti.
Best actress may go to Lily Gladstone of "Killers of the Flower Moon," the real-life story about a murder plot to take over lucrative Osage oil rights in 1920s Oklahoma. If she prevails, Gladstone would be the first Native American actress to win an acting Oscar.
Gladstone's rivals include previous Oscar winner Emma Stone, nominated this year for playing a woman revived from the dead in the dark and wacky comedy "Poor Things."
The supporting actor race features "Oppenheimer" star Robert Downey Jr., who played the scientist's professional nemesis, and Sterling K. Brown from "American Fiction."
Da'Vine Joy Randolph, praised for her role as a grieving mother in "The Holdovers," vies for best supporting actress against Danielle Brooks from "The Color Purple" and others.
"Barbie," last year's No. 1 film with $1.4 billion in global ticket sales, may be shut out of the top awards. Billie Eilish's "Barbie" ballad "What Was I Made For?" is likely to win the original song prize, Feinberg said, and could snag the awards for costumes and production design.
For Nolan, the night could bring his first directing Oscar, as well as the award for adapted screenplay. The director of "The Dark Knight" trilogy, "Inception" and other acclaimed films has never had a movie win best picture.
The ceremony may end with "the industry-wide coronation for Christopher Nolan," Feinberg said. With "Oppenheimer," "he has made his best possible argument yet for why he is worthy of this recognition."
