LOS ANGELES -- The 50 comeback concerts Michael Jackson planned in London last summer sold out in a few hours.

With those shows relegated to what-if status by his death in June, the question now is how well the singer can pack movie theaters with "Michael Jackson: This Is It," a chronicle of his concert preparations that now stands as his final performance.

Advance ticket sales have been brisk, but no one has a handle on how big the turnout might be this week.

Some think it's likely to surpass the $31.1 million opening weekend and the $65.3 million lifetime haul of "Hannah Montana & Miley Cyrus: Best of Both Worlds Concert," the biggest concert movie on record.

Some expect a $100 million total domestic haul. Others think it could go much higher, but how high is anyone's guess.

"It reminds me of 'Blair Witch,' it reminds me of 'Fahrenheit 9/11,' it reminds me of 'Passion of the Christ.' You even have to throw in 'Snakes on a Plane.' Films that are bigger than life and just unpredictable. We don't really know how they're going to do," said Paul Dergarabedian, box-office analyst for Hollywood.com.

For the record, "The Blair Witch Project," ''Fahrenheit 9/11" and "The Passion of the Christ" all were hits. "Snakes on a Plane," despite tremendous advance buzz, fizzled.

Not quite a concert film, not quite a documentary, "This Is It" is like nothing that has hit theaters before. It comes just months after Jackson's death, with fans still eagerly digesting every scrap of news about him. It distills more than 100 hours of footage shot as Jackson rehearsed for the concerts in the weeks before his death. And it truly is a final glimpse of an artist who ruled the pop charts in the 1980s before retreating to a reclusive life amid allegations of child molestation.

Distributor Sony is treating the film like the crown jewels, keeping it under wraps until the big blowout Tuesday night, when there will be simultaneous premieres worldwide, followed by advance screenings for paying customers ahead of Wednesday's official theatrical debut.

No critics have seen it, and entertainment journalists were shown only 12 minutes of footage last week before interviews with the filmmakers.

Sony, which paid $60 million for the film rights, plans to have the movie out for just over two weeks, lending it some of the exclusivity of Jackson's aborted concert stand in London.

"We think the 16 days is right. It's sort of a special event that you want to frame in a special way," said Rory Bruer, head of distribution for Sony.

If business really takes off, Sony could extend the film's run, as Disney did with Cyrus' concert movie, which originally was scheduled for only a one-week leg in theaters.

Concert films historically have been a niche genre, with only a few finding a lasting audience in theaters or on home video, among them "Woodstock," ''Monterey Pop," ''Madonna: Truth or Dare," the Rolling Stones' "Gimme Shelter" and "Shine a Light," The Band's "The Last Waltz," the Talking Heads' "Stop Making Sense" and "U2: Rattle and Hum."

Box-office results for concert flicks have been petty cash compared to blockbuster action films and comedies, with last March's "Jonas Brothers: The 3D Concert Experience" running a distant second to Cyrus' film in the record books, topping out at $19.2 million.

The Batman blockbuster "The Dark Knight" took in $67.2 million on opening day, more than Cyrus' concert movie did in its entire run.

"This Is It" opens in about five times as many theaters as Cyrus' movie, which played in only 683 cinemas because of the limited number equipped to show digital 3-D films.

Advance ticket sellers Fandango.com and MovieTickets.com report that sales for "This Is It" are running about where Cyrus' film was days before its release.

Comparisons between the two movies are dicey, though. Fans of Jackson, who was 50, are much older than Cyrus' and generally less inclined than young audiences to make the trek to movie theaters. Yet Cyrus does not have the huge global appeal of Jackson, whose film is opening in virtually every country at the same time.

"As big as she is, I don't think she holds a candle to Michael Jackson around the world," said Walt Borchers, senior vice president of sales and marketing for MovieTickets.com.

And, added Borchers, the fact that Jackson now is out of reach deepens his film's appeal.

"Miley, you could have seen her in concert. Now nobody is able to see Michael Jackson in concert. On this film, that does add some fervor," Borchers said.

Based on the initial fervor when tickets first went on sale in late September, Fandango.com expected that "This Is It" easily would shoot past the box-office receipts of Cyrus' movie, said Rick Butler, chief operating officer.

Since then, though, sales have leveled off, so it's uncertain Jackson's movie will hit that mark, Butler said.

The movie's durability ultimately will come down to how good a performance Jackson gives, Butler said. In trailers and the footage shown to reporters last week, Jackson was in prime musical form.

"It's all going to be about his voice. How good does he sound? And boy, the voice sounds as good as it ever did," Butler said. "There's no reason to believe that whatever snippets they've given us for whatever of his songs, he won't sound that way with everything in his repertoire."