2009 releases earning big, but why?

Domestic B.O. for January and February was up 13%. Admissions rose nearly 10%. With a slew of high-profile projects set to open in the next two months, Hollywood hopes to maintain this torrid pace.

But the studios’ good fortune comes with vexing questions: Why is this happening, and how on earth do they keep it up?

The past few weeks have been full of theories as to why the public has taken an interest in the normally dormant early months of the year. The most frequent explanation is that a recession-weary populace has been anxious for an escape. But there’s also the fact that studios, flush with product from the days when hedge fund money flowed into Hollywood, just needed a place to put their movies — and audiences welcomed the product.

In the past four years, private equity money flowed into Hollywood, creating a surplus of movies and forcing studios to rethink their long-established release patterns.

It has required Hollywood to start something it had previously paid lip service to: a genuine year-round calendar, where high-profile releases are dispatched on weekends that used to be box office dumping grounds.

Traditionally, studios have saved their heavyweight titles for Easter, summer and year-end holidays.

Partly this is due to timidity — with huge sums of money riding on a film, you have to play it safe — and partly it’s because talent always insisted on long-established key opening dates.

But with an overcrowded release schedule, studios have begun launching more prominent films in off-peak months, and audiences have responded with enthusiasm.

For the first time ever, three films — Warners’ “Gran Torino,” Sony’s “Paul Blart Mall Cop” and 20th Century Fox’s “Taken” — made more than $100 million between Jan. 1 and Feb. 28. Fox Searchlight’s “Slumdog Millionaire” nearly hit that mark, and its overseas tallies sent it soaring past $200 million.

While conventional wisdom says showbiz is recession-proof, many doubted whether the current economic crash would lead to a surge in moviegoing, because audiences have so many other entertainment options.

Studios hope that the increased filmgoing will maintain its momentum.

“You are going to have a lot of goodwill built upon on the part of moviegoers,” said Disney prexy of domestic distribution Chuck Viane. “It also means more people are seeing trailers for summer films.”

But before you think that the studios have found the formula for a year-round box office nirvana, consider this: The fiscal crunch has slowed up hedge-pics, and the 2008 WGA strike, along with fears of a SAG walkout, have severely slowed production. That means next year’s slate may be underpopulated.

So Hollywood will have to confront the fact it may have created its own speed bump for the fast-moving B.O. buildup.

Moreover, the idea of a year-round box office will be tested further in the near term, as studios release a spate of films in the coming months that approach the level of summer blockbusters.

“The audience has gotten into the rhythm of going to the movies. There’s been a constant flow of attractive product since Christmas,” Paramount co-chair Rob Moore says.

Hot on the heels of the March 6 bow of Zack Snyder’s “Watchmen,” there are Dwayne Johnson family pic “Race to Witch Mountain” (March 13), Julia Roberts-Clive Owen starrer “Duplicity” (March 20), DreamWorks Animation’s “Monsters vs. Aliens” (March 27), “Hannah Montana: The Movie” (April 10), and “State of Play” (April 17).

Over the decades, there have been plenty of winter and spring hit pics, but Hollywood usually dismissed them as flukes. There’s never been this sort of sustained winning streak. Films are seeing huge multiples, since they have less competition than they would in summer.

Partly the studios have been emboldened by the success of other pics in off-peak slots.

Warner Bros.’ “300,” which looked an awful lot like a summer tentpole, debuted in early March 2006 to $70 million, with a domestic cume of $210.6 million and $456.1 million worldwide — the biggest number ever for a March pic. Last year, Warners went for it again, opening Roland Emmerich’s “10,000 B.C.” the same weekend in March. The pic cumed $94.8 million domestically and $269.8 million worldwide.

This year, studio opened Snyder’s “Watchmen” in the same frame.

In January, Twentieth Century Fox caught the competish off-guard by opening “Taken” over Super Bowl weekend. No one had ever dared open a male-driven actioner on that date. Yet it worked.

“Now, every studio is going to look at Super Bowl weekend differently,” one exec says.

Fifteen years ago, summer box office began post-Memorial Day. Now, the season begins the first weekend in May.

Last year, when Jeffrey Katzenberg announced Paramount would release the 3-D “Monsters vs. Aliens” on March 27, he quipped that summer now begins the end of March.

Katzenberg’s hand was forced to some degree. “Monsters” was scheduled to open in May, but then Fox dated James Cameron’s 3-D “Avatar” for the same month, meaning too few 3-D screens for one of the films. (Fox subsequently pushed “Avatar” back to December.”)

There’s a huge silver lining to the move: “Monsters” gets out of the way of Fox’s family pic “Night at the Museum: Battle of the Smithsonian,” which opens May 22.

Fox helped pioneer the spring toon-tentpole with the “Ice Age” duo and last year’s “Dr. Seuss’ Horton Hears a Who.” The three films respectively cumed $195 million, $176.4 million and $154.2 million domestically.

Universal prexy of distribution Nikki Rocco has been a longtime proponent of a year-round calendar. She has no misgivings about the studio’s decision to move the release of “Fast and Furious 4″ from June 12 to April 4.

“Why not? With a sequel that’s a built-in franchise, it gives you playability that the summer doesn’t afford because it’s such a crowded marketplace,” Rocco says.

U also opted to debut Russell Crowe-Ben Affleck-Rachel McAdams topliner “State of Play” on April 17.

One exec maintains that a key remaining challenge is convincing filmmakers and talent that it can be a good thing to avoid summer. “Part of the issue is perception. Talent thinks that a studio doesn’t believe in their movies.”

Last year, Disney had a blockbuster hit with the 3-D limited run “Hannah Montana/Miley Cyrus: The Best of Both Worlds Concert Tour,” which opened to $31.1 million in early February on its way to $65.3 million domestically.

This year, Disney followed with “Jonas Brothers: The 3D Concert Experience,” which had a solid, but unspectacular, opening of $12.5 million over the Feb. 27-March 1 weekend. The Mouse House opens “Hannah Montana: The Movie” on April 10. The studio also has “Race to Witch Mountain.”

Follow @Variety on Twitter for breaking news, reviews and more