That surpasses the record set in 2006 by "Pirates of the Caribbean: Dead Man's Chest," which took 16 days to make $300 million.
The latest Batman installment already had broken records for best opening weekend at $158.4 million and best single-day with $66.4 million. It's also busted records in its showings on IMAX screens, making $16.3 million in its first 10 days.
Fellman expects that "Dark Knight" could reach $400 million in about 18 days, which would beat the record "Shrek 2" set in 2004 when it made that much money in 43 days.
"What can you say? We've been getting a lot of repeat business coming in," Fellman said. "Our audience is expanding, like you would expect with terrific word-of-mouth and strong reviews. Our audience is getting a little bit older, that's the good news. We're finding the younger demographic, male and female, coming back."
"It is a big surprise to us," he added. "To say we would have done $300 (million) would have been a fabulous gross for another Batman movie. To do $300 (million) plus in 10 days, we just couldn't have predicted it."
"The Dark Knight" could pass "Titanic" as the highest-grossing film in U.S. history, said Paul Dergarabedian, president of Media By Numbers. The mother of all blockbusters, James Cameron's 1997 extravaganza made $600,788,188 domestically, a record no other movie has come close to touching.
"The `Titanic' record has sat in a lock box for 10 years. It's a tall order but if any film has a chance to surpass that number, it's got to be `Dark Knight,"' he said. "The notion that it could beat `Titanic' is not all that far-fetched anymore."
Director Christopher Nolan's follow-up to his 2005 origin story "Batman Begins," which again stars Christian Bale as the tormented comic-book crime fighter, initially benefited from the mystique of the late Heath Ledger giving his masterful, last performance as the Joker, Dergarabedian said.
"Now, it's all about word-of-mouth," he said. "The first weekend, there was this huge, pent-up demand and eagerness by audiences to see this movie. Now, it's like a freight train -- it seems to be unstoppable."
Part of the film's visual allure comes from the fact that 30 minutes of it were shot with IMAX cameras, including the elaborate bank-heist scene at the start.
"Chris (Nolan) has clearly hit upon something," said Greg Foster, chairman and president of IMAX Filmed Entertainment. "There are many important filmmakers who we've spoken with in the last couple of weeks about shooting with IMAX cameras."
Coming in second place was "Step Brothers," which had a strong opening of its own with $30 million. The comedy reunites Will Ferrell and John C. Reilly, co-stars of "Talladega Nights: The Ballad of Ricky Bobby," as 40-year-olds who've never left home and are forced to share a bedroom when their parents get married.
Rory Bruer, head of distribution for Sony, said this was at the high end of the studio's expectations.
"It really is a terrific start. We'd hoped to be in the mid-to-high $20 (millions), so to hit $30 (million) is a great start," Bruer said. "Having the chemistry of Will Ferrell and John C. Reilly together again, reuniting with (director) Adam McKay who did `Talladega Nights,' it's great. They both immerse themselves and the humor comes from their connection."
Sony also has the Will Smith superhero flick "Hancock," which made $8.2 million this past weekend to cross the $200 million mark.
The weekend's other big release was "The X-Files: I Want to Believe," which made an estimated $10.2 million. Ten years after the first "X-Files" movie and six years since the pioneering sci-fi show went off the air, this latest installment finds Mulder (David Duchovny) and Scully (Gillian Anderson) re-teaming to solve a missing-persons case.
"It opened within our reasonable expectations. Our low range was $10 (million), our high range was $15 (million)," said Chris Aronson, distribution executive for 20th Century Fox. "I read some `X-Files' fan sites and the postings on there were incredibly positive about the film. The hardcore `X-Files' fans, they're happy. And frankly, that's who the movie was made for."
Estimated ticket sales for Friday through Sunday at U.S. and Canadian theaters, according to Media By Numbers LLC. Final figures will be released Monday.
1. "The Dark Knight," $75.63 million.
2. "Step Brothers," $30 million.
3. "Mamma Mia!" $17.9 million.
4. "The X-Files: I Want to Believe," $10.2 million.
5. "Journey to the Center of the Earth," $9.4 million.
6. "Hancock," $8.2 million.
7. "WALL-E," $6.3 million.
8. "Hellboy II: The Golden Army," $4.9 million.
9. "Space Chimps," $4.4 million.
10. "Wanted," $2.7 million.
Universal Pictures, Focus Features and Rogue Pictures are owned by NBC Universal, a unit of General Electric Co.; Sony Pictures, Sony Screen Gems and Sony Pictures Classics are units of Sony Corp.; DreamWorks, Paramount and Paramount Vantage are divisions of Viacom Inc.; Disney's parent is The Walt Disney Co.; Miramax is a division of The Walt Disney Co.; 20th Century Fox, Fox Searchlight Pictures and Fox Atomic are owned by News Corp.; Warner Bros., New Line, Warner Independent and Picturehouse are units of Time Warner Inc.; MGM is owned by a consortium of Providence Equity Partners, Texas Pacific Group, Sony Corp., Comcast Corp., DLJ Merchant Banking Partners and Quadrangle Group; Lionsgate is owned by Lionsgate Entertainment Corp.; IFC Films is owned by Rainbow Media Holdings, a subsidiary of Cablevision Systems Corp.