Actors make up the largest branch of the Academy of Motion Picture Arts and Sciences, so SAG members have perhaps more sway in determining Oscar winners than any other group.
This year, the five nominees for SAG's top honour, outstanding performance by a movie cast, are: 12 Years a Slave, American Hustle, Dallas Buyers Club, August: Osage County and Lee Daniels' The Butler.
Obviously, SAG and the academy don't always agree: Neither August: Osage County nor The Butler were nominated for best picture, and The Butler was snubbed entirely.
The effects-heavy, sparsely peopled Gravity was predictably overlooked by SAG (except for a best actress nomination to Sandra Bullock), while it garnered 10 Oscar nods.
But the SAG Awards will give a window into support for Oscar favourites 12 Years a Slave and American Hustle.
In individual honours, SAG favoured 12 Years, nominating Chiwetel Ejiofor, Michael Fassbender and Lupita Nyong'o.
Jennifer Lawrence, for supporting actress, is the lone American Hustle nominee.
The SAG outstanding cast awards have lined up with Oscar best-picture winners, including Argo, The King's Speech, Slumdog Millionaire and No Country for Old Men.
But SAG diverged in the past with picks like The Help, Inglourious Basterds and Little Miss Sunshine.
Oscar upset
The actors did foretell one of the biggest Oscar upsets in 2005, choosing Crash over Brokeback Mountain.
But the SAG Awards also represent one of the more collegiate atmospheres of awards season, with winners almost uniformly expressing gratitude for an honour chosen by their peers. The speeches are often good, too, and can help stoke Oscar support.
Among the nominees Saturday night are Cate Blanchett (Blue Jasmine), Matthew McConaughey (Dallas Buyers Club), Forest Whitaker (Lee Daniels' The Butler), Meryl Streep (August: Osage County), Tom Hanks (Captain Phillips), Emma Thompson (Saving Mr Banks) and Bruce Dern (Nebraska).
James Gandolfini was nominated posthumously for his supporting performance in Enough Said.
Among SAG's TV drama ensemble contenders are HBO's Boardwalk Empire and Game of Thrones, AMC's Breaking Bad, PBS's Downton Abbey and Showtime's Homeland.
Comedy series ensemble nominees include NBC's 30 Rock, Netflix's Arrested Development, CBS's The Big Bang Theory, ABC's Modern Family and HBO's Veep.
SAG's lifetime achievement award will be given to Rita Moreno, the 81-year-old West Side Story actress whose career has spanned Broadway, television and music.