While I had no problem with Mahershala Ali winning an Oscar for his performance in “Green Book” this year, I did have a problem with the fact that he was nominated as best supporting actor.

As anyone who has seen the film knows, Ali’s character, Don Shirley, is on the screen for most of the movie. While it can be argued that the film focuses more on Viggo Mortensen’s character, Frank Vallelonga, that doesn’t mean that Ali’s character should be considered a supporting part. Note that Mortensen is on the screen only 16 minutes longer than Ali in a movie with a running time of over two hours. If Ali’s role is not a leading role, than what is?

For more blurring of the distinction between leading and supporting roles, consider “The Favourite,” where Olivia Colman won the Oscar as best actress this year while Rachel Weisz and Emma Stone were deemed supporting actresses and competed against each other in that category for the Academy Award. They both lost to Regina King (“If Beale Street Could Talk”).

Again, it can be argued that movie focuses more on Colman’s character, Queen Anne, than her two rivals. Yet once again, look at the screen time. In this two-hour film, Stone is on the screen for 56 minutes, Colman 47 and Weisz 44. They should have all been competing against each in the best actress category.

But that’s not how it works in Hollywood where how leading and supporting roles are determined has more to do with politics than logic. In fact, no concrete rules exist pertaining to the amount of screen time necessary to determine whether a role is leading or supporting.

Typically, studios decide who should be designated leading and supporting based on who they believe has the best chance getting nominated for an Oscar. The Academy doesn’t help matters since it has placed no restrictions for determining what is a leading and a supporting role. The ultimate decision belongs to the Academy voters, which is why studios mount such vigorous “for your consideration” campaigns for their favored thespians.

For more leading vs. supporting role discrepancies, Jeff Bridges has considerably more screen time than Ben Johnson in “The Last Picture Show” and should have been nominated as best actor. But he was nominated for best supporting actor instead and competed against Johnson, who won the Oscar even though he’s on screen only 10 minutes.

Marlon Brando, meanwhile, won the best actor Oscar for “The Godfather,” for less than an hour of screen. His co-star Al Pacino has far more screen time and thus should have been nominated for best actor instead of best supporting actor, where he lost to Joel Grey (“Cabaret”).

OK, we shouldn’t necessarily equate screen time with quality of performance but one could reasonably argue that Bridges and Pacino got robbed. To play devil's advocate, Johnson had been in the film business for nearly 40 years without a single Oscar nod before “The Last Picture Show” and Brando is, well, Brando. At the time, both Bridges and Pacino were up-and-comers, not established stars. And yes, Johnson and Brando gave impressive performances.

For one more example – and there are plenty of others, James McAvoy is on the screen longer than Forest Whitaker in “The Last King of Scotland,” but it’s Whitaker who received the best actor nomination and Oscar for his portrayal of Ugandan dictator Idi Amin. McAvoy, who played Amin’s physician, received no nomination, not even in the best supporting actor category. Granted, Whitaker’s role is just a tad meatier than McAvoy’s. That his character was fictional probably didn’t help matters. And, again, Whitaker’s performance was certainly Oscar worthy.

At least most of these thespians were on screen longer than half an hour with the exception of Johnson. He got his Oscar for 10 minutes of screen time. He doesn’t hold the record, though. That belongs to Beatrice Straight, who won the best supporting actress Oscar for 5 minutes of work in "Network."

Other best supporting actress Oscar winners with minimal screen time include Judi Dench (8 minutes in “Shakespeare in Love”), Gloria Grahame (9 minutes in “The Bad and the Beautiful”), Ingrid Bergman (14 minutes in “Murder on the Orient Express”), Kim Basinger (15 minutes in “L.A. Confidential”), Penelope Cruz (15 minutes in “Vicky Cristina Barcelona”), Anne Hathaway (15 minutes in “Les Miserables”), Tilda Swinton (18 minutes in “Michal Clayton”) and Lee Grant (18 minutes in “Shampoo").

Johnson’s 10 minute-performance in “The Last Picture Show” holds the record for the shortest amount of screen to win a best supporting actor Oscar. He bests Jack Palance (12 minutes in “City Slickers”), Alan Arkin (14 minutes in “Little Miss Sunshine”), Jason Robards (14 minutes in “All the President’s Men”), Jared Leto (21 minutes in “Dallas Buyers Club") and Anthony Quinn (23 minutes in “Lust for Life”).

The record for winning the best actress Oscar with the briefest amount of screen time belongs to Nicole Kidman, who nabbed her statuette for her 28-minute performance in “The Hours.”

The record for winning the best actor Oscar with the briefest amount of screen time belongs to David Niven (15 minutes in “Separate Tables”) narrowly beating out Anthony Hopkins (16 minutes in “The Silence of the Lambs”).

Oscar nominees in the best supporting actress categories with limited screen time include Ruby Dee (10 minutes in “American Gangster” – the winner was Swinton), Viola Davis (8 minutes in “Doubt” – the winner was Cruz) and Hermione Baddely (2 minutes in “Room at the Top” – the winner was Shelley Winters in “The Diary of Anne Frank”). Sylvia Miles hit the downscale double, though, receiving an Oscar nomination for a six-minute performance in "Midnight Cowboy" and another Oscar nod for an eight-minute performance in "Farewell, My Lovely." In the former race, she lost to Goldie Hawn in "Cactus Flower" and in the latter Lee Grant triumphed in "Shampoo."    

I should note that I relied on numerous sources for this column. It's quite likely that some actors and actresses with minimal screen time were not mentioned. I'll gladly add any omissions in my next column. And that's the long and short of it.