Greg Mottola knows geeks. He’s chronicled their lives for much of his 15-year career, from the freshman-dorm series “Undeclared” and high school outcast comedy “Superbad” to his coming-of-age tale “Adventureland.” So when acting/writing team Simon Pegg and Nick Frost went helmer hunting for their sci-fi road trip comedy “Paul,” the story of two Comic-Con attendees who befriend a snarky alien (voiced by Seth Rogen), they knew they’d found the right fanboy.

“I was a childhood sci-fi comicbook fanatic,” confesses Mottola, who attended the March 13 North American preem of “Paul” at SXSW. “When Simon and I met, we had our little geek bonding.”

The collaboration, however, is far from left of center — it’s the biggest mainstream gamble of their careers. Modest by sci-fi standards, the $45 million Universal/Relativity/Working Title/Big Talk film is a quantum leap from Mottola’s $60,000-budgeted debut, “The Daytrippers,” or even his $20 million “Superbad,” and several times the cost of the Pegg/Frost-toplined spoofs “Shaun of the Dead” and “Hot Fuzz.”

Mottola has alternated between self-penned indies and studio films written by others, a one-for-me, one-for-them pattern that isn’t entirely accidental. His planned sophomore feature, “Life of the Party,” the darkly comic tale of an intervention (“It’s the Charlie Sheen story,” he jokes), was greenlit by Columbia in 1998 before quickly going into turnaround due to concerns over the depressing subject matter.

“After it fell apart, I got a little psyched out, and, ultimately, frustrated,” he recalls. “Whatever little steam I had from making one small indie film kind of evaporated. So when the opportunity came my way to direct other people’s writing, I pounced. As time passed, I realized I equally love arthouse and Hollywood movies, and I don’t want to miss out on a chance to do both.”

The experience of making a movie with a third of the budget going to special effects came with a host of new challenges. To get “Paul” greenlit without proven big box office leads, Mottola had to cut weeks from the shoot, scale back some action sequences, forego a second-unit crew and spend 18 months in post as part of a deal with CGI house Double Negative to create the title alien character at a lower cost.

He was asked to hire recognizable American comic actors like Jason Bateman, Kristen Wiig and Bill Hader to round out the cast. “That’s what we wanted to do anyway,” he says. “They were all people I’d worked with before and were fans of Simon and Nick, so it didn’t feel like a compromise.”

Mottola snagged cameos from Sigourney Weaver, Jane Lynch and the voice of Steven Spielberg, who suggested the idea of playing himself asking alien Paul advice about “E.T.” The film also reunites Mottola with Rogen, who starred in “Undeclared” and co-wrote “Superbad,” both Judd Apatow productions.

Mottola is penning romantic novel adaptation “Important Artifacts” for Natalie Portman, Paramount and Brad Pitt’s Plan B Entertainment.

“It’s a writing-only gig that doesn’t have a director, so I may throw my hat in the ring, and there’s a slight chance Pitt might want to be in it,” he says.

He also hopes to free his “Party” script from legal entanglements. But for now, it’s all about SXSW.

“I was the first one to bring it up, because I just love that festival. It has a good sensibility for the movie,” he says.”Austin is quite a geek-friendly town.”