Surprise hits like "The Devil Wears Prada" are by their very nature tricky to forecast: They defy or exceed expectations, showing legs at the box office as more moviegoers discover them. Usually, there's a good reason why they aren't considered obvious hits from the outset. Maybe the genre is considered limited, the story too quirky or the stars not big enough.

This summer, there are a number of comedies and original stories that could turn into sleeper hits. Just don't ask studio execs to identify them.

"It's hard to predict your sleepers because that's what they are," says Warner distribution chief Dan Fellman.

"This summer we are pretty much on the nose with our movies," he adds. "Everyone knows what 'Sex and the City' is."

This far out, another distribution exec points out, it's hard to gauge true potential of rival releases. And when it comes to their own films, studios tend to be big believers: They wouldn't be making the movies if they didn't see the box office potential in them. Others might be surprised by their success, but they are not.

Universal, for example, is very high on "Get Him to the Greek" and "MacGruber," two early summer comedies. "Greek," bowing June 4, stars Russell Brand as a debauched has-been rocker that Jonah Hill's character must ferry back to the Greek Theater for a comeback concert. Produced by Judd Apatow, who exceeded expectations with "Knocked Up" and "Superbad," the comedy is directed by "Forgetting Sarah Marshall" helmer Nicholas Stoller. Brand is not a huge star stateside but could become one; he certainly stole the show in "Forgetting Sarah Marshall."

"MacGruber," a bigscreen adaptation of the "Saturday Night Live" parody of "MacGyver," stars Will Forte as the special operative. Originally slated for April, the Rogue picture will compete head to head with "Shrek Forever After" as counterprogramming. "MacGruber" is a known commodity thanks to "SNL," but box office success is by no means a foregone conclusion considering the uneven performance by previous "SNL" adaptations.

"Dinner for Schmucks" features even more comedy firepower: It stars Paul Rudd as an exec that brings Steve Carell to his boss' "dinner for idiots."Jay Roach directed Paramount's July 23 release. But the source material? A 1998 French film -- a fact that could be held against it.

Columbia, meanwhile, seemingly has a challenge in "The Karate Kid," debuting June 11 opposite another 1980s remake, "The A-Team." The original "Karate Kid" franchise, launched in 1984 with Ralph Macchio and Pat Morita, was a bit hokey; the last attempt to revive it with Hilary Swank as "The Next Karate Kid" miffed horribly. But the latest attempt stars Will Smith's son Jaden and features Jackie Chan as his martial arts mentor and "The Curious Case of Benjamin Button" star Taraji P Henson as the Kid's mom. As one rival advised, anything with the son of Will Smith has great potential.

Katherine Heigl, who has shown an ability to exceed summer expectations with "Knocked Up" and "The Ugly Truth," returns the bigscreen June 4 in Lionsgate's "Killers," another romantic comedy. This time out she's a happily married woman who must dodge would-be assassins of her husband, a former assassin played by Ashton Kutcher. The director? None other than "Ugly Truth" helmer Robert Luketic.

Later in the summer, Julia Roberts returns with "Eat, Pray, Love," a bigscreen adaptation of Elizabeth Gilbert's bestselling memoir. Gilbert's search for meaning in the wake of divorce resonated with women, especially of a certain age, but will it cross over? That's what Hollywood will find out Aug. 13 when Columbia releases it.

But what, if anything, will turn into this summer's "Little Miss Sunshine"? Could it be "Cyrus," another Fox Searchlight film? Jay and Mark Duplass directed the pic, about a divorced man (John C. Reilly) who must contend with the overprotective son (Jonah Hill) of new love (Marisa Tomei). Slotted in July, it debuted at Sundance this year.