Despite its brisk pace, "The Dark Knight" is not expected to approach the total for "Titanic," which put up smaller numbers week after week but lingered at the top of the box office for months.
Dan Fellman, head of distribution at Warner Bros., said he expects "The Dark Knight" to finish at about $530 million, though it could reach $550 million if business persists as strongly as it has.
"I keep raising the number because it just keeps holding better than expected," Fellman said.
"The Dark Knight" will climb to about $505 million by Labor Day, the conclusion of Hollywood's busy summer season. That amounts to nearly one-eighth of Hollywood's overall summer revenue of $4.2 billion, which edges the previous summer record of $4.18 billion set last year, according to box-office tracker Media By Numbers.
Factoring in today's higher admission prices, "The Dark Knight" would need to take in about $900 million to match the number of tickets sold by "Titanic."
Labor Day weekend was generally sleepy at theaters, with a rush of new movies failing to find much favor with audiences. Through Sunday, Paramount's comedy "Tropic Thunder" remained No. 1 for the third straight weekend with $11.5 million.
The 20th Century Fox sci-fi thriller "Babylon A.D." with Vin Diesel debuted in second place with $9.7 million, while Overture Films' espionage drama "Traitor," starring Don Cheadle, opened at No. 5 with $7.9 million.
Premiering at No. 7 was Lionsgate's spoof flick "Disaster Movie" with $6.2 million. MGM's campus comedy "College" opened well outside the top 10 with $2.1 million.
The top 12 movies took in $75.2 million, down 23 percent from the same weekend last year, when "Halloween" opened with $26.4 million.
"This is kind of an inauspicious end to a really incredible summer," said Paul Dergarabedian, president of Media By Numbers. "We limped past the finish line."
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