When it opens in theaters this weekend, The Dark Knight is expected to become a very bright spot in the summer of Warner Bros. executives.

For one thing, the buzz generated by the death of star Heath Ledger, who plays the Joker character, will draw legions of Ledger fans that might otherwise have been inclined to ignore the many comic-strip-inspired flicks that litter the summer season.

But The Dark Knight is also the latest in a string of flicks to try to play its PG-13 rating both ways, simultaneously luring family audiences with a low rating but pushing the envelope, in terms of acceptable levels of carnage, to keep older teens and young adults interested.

"This is probably the darkest Batman film ever made, with almost nonstop violence," says Jeff Bock, who analyzes box-office sales for Exhibitor Relations, a Los Angeles-based entertainment-research firm.

Bock cites last year's Die Hard movie, as well as this summer's Iron Man and Hellboy II: The Golden Army, as films that demonstrate the increasing violence that's slipping into movies rated as safe for preteens.

Like those films, "Five or six years ago, The Dark Knight would have been rated R," says Bock.

Critics seem to agree: Advance reviews have made much of the film's "sadism," "perversity," and "hyperviolence."

That isn't likely to stop The Dark Knight, the second film in director Christopher Nolan's revitalized Batman franchise, from reaping up to $100 million from devout Batman fans in its opening weekend, Bock predicts—and the box-office take for the movie could climb even higher if parents do prove willing to bring their tweens along.

The big question in the minds of studio executives, of course, is whether this movie—certainly the most anticipated of the year and one which has benefited from almost constant media attention since Ledger's death in January—can top Spider-Man 3. Spidey opened in May of 2007 to the tune of $151 million, according to the industry website BoxOfficeMojo.com, making it the single largest movie opening of all time.

Bock said he thinks The Dark Knight is unlikely to match that.

Spider-Man 3 opened against a relatively weak slate of springtime movies, none of which presented much competition at the box office. The Dark Knight, on the other hand, is opening midsummer when lots of films are still making money. Universal's The Mummy, another predicted summer hit which opens August 1, could eat into repeat viewings. In worse news, The Dark Knight is opening against Mamma Mia, which has broken opening records in overseas markets.

And despite the family-friendly PG-13 rating, repeat viewings by Mom, Dad, and Junior seem doomed.

"I like a comic-book movie with a few laughs," says Bock. Despite the hype, "The Dark Knight is not offering that up."