It was business as usual at the 2011 international box office. And business is booming.

Last year, total overseas B.O. skyrocketed to approximately $23.5 billion through Dec. 31, up about 11% from the $21.2 billion earned in 2010 (the first time a year’s international ticket sales reached the $20 billion mark).

Of that total, the Hollywood majors took in an estimated $13.52 billion internationally in 2011 vs. 2010’s $12.7 billion collective studio tally.

While international’s influence on the domestic film biz is nothing new, the year saw increased signs of that impact, including distribution of several films launching weeks or even months ahead of their domestic releases. Moveover, the success of the 3D format overseas helped justify Hollywood’s continued interest, since it more than offset 3D’s waning U.S. popularity.

The growth in overseas box office — thanks in large part to burgeoning markets like China and Russia — reps a trusty fallback for studios and film distributors around the world, especially as domestic B.O. struggles to match 2009’s record tally of $10.6 billion. (2011 recorded $10.2 billion domestically.)

In 2011, Hollywood launched several summer biggies overseas, with “Thor” and “Fast Five” bowing as early as two weeks ahead of the U.S. “Thor,” from Paramount and Marvel Entertainment, topped out at nearly $450 million globally, with $268 million from foreign wickets. “Fast Five” became one of Universal’s highest-grossing pics ever, with $419 million internationally for a total $629 million worldwide.

And while neither was released in 3D, the format continues to grow overseas — despite frequently higher 3D upcharges over-seas than those in the States, making pricey conversions or 3D shoots worthwhile.

Sony-Paramount’s 3D motion-capture toon “The Adventures of Tintin: The Secret of the Unicorn” represented both the early launch and 3D trends. Capitalizing on “Tintin’s” European origins, the pic had an unusual two-month overseas headstart before bowing Stateside on Dec. 23. The movie grossed more than $240 million internationally by Dec. 31.

A handful of sure-fire franchises met or surpassed expectations in 2011.

The year’s top three worldwide grossers, Warner Bros.’ record-breaking “Harry Potter” finale, Par’s “Transformers: Dark of the Moon” and Disney’s “Pirates of the Caribbean: On Stranger Tides,” each reached $1 billion, making it the first year in which three films hit that mark.

China and Russia — one-half of the BRIC quartet, which also includes growing markets Brazil and India — scored bellwether B.O. totals.

In China, local box office surged past $2 billion for the first time, a 29% increase over 2010. That market, with its government-imposed cap of 20 imported films, has been growing year-over-year by at least 25% since 2003. (2010 overall Chinese B.O. came in 64% ahead of the previous year.)

“The rise of small- and medium-budget pics is challenging the dominance of blockbusters in the Chinese film market,” says Tong Gang, head of the film bureau at the State Administration of Radio, Film & TV, noting that a group of young filmmakers has emerged that have contributed to the burgeoning box office.

That mix of top-performing local product, such as Zhang Yimou’s Christian Bale starrer “The Flowers of War,” and Hollywood fare, led by “Transformers” and “Kung Fu Panda 2,” is helping grosses soar in China, while in Russia, studio pics — including B.O. topper “Pirates of the Caribbean: On Stranger Tides” ($63.6 million) and “Puss in Boots” ($50.3 million), frequently do boffo biz, while locally produced films continue to struggle.

Russian B.O. in 2011 clocked in at $1.16 billion, a 20% rise over 2010, though local pics accounted for just 14.7% of the total, down from 2010’s 15.3% share. (Brazilian B.O. improved 12%; Indian figures weren’t available due to the regionalized reporting system on the Subcontinent.)

“This year will again be the American year in Russian cinema, simply because Hollywood does it better,” notes Alexander Semenov, founder and publisher of Russian Film Business Today.

China and Russia rep two of the fastest-developing moviegoing markets in terms of infrastructure.

Two years ago in Russia, studios were able to secure at most 500 screens for a single run. Now, that screen potential has tripled, with more than 2,500 modern movie screens available. In China, a film can play on upwards of 7,000 screens, with the country’s screen count having risen 33% over 2010, totaling approximately 9,200 in 2011.

There’s also an increased number of multiplexes being installed in smaller Eastern European markets.

Cinema City Intl., Central and Eastern Europe’s largest theater chain, plans to double the number of plexes in Romania, for instance, from 12 to 24 through 2013. (Romanian B.O. was up a hearty 20% year-over-year during the first three quarters of 2011.)

While franchise titles continued to post top results around the world, last year saw American comedies grab standout box office.

“It’s extremely rare to see an American comedy earn more than $100 million overseas,” says one distribution exec.

Still, Warner’s “The Hangover Part II” benefited from its predecessor’s worldwide popularity, and was 2011’s top-grossing comedy with $320 million internationally, and “Bridesmaids” surpassed $100 million at the overseas wickets.

A pair of Sony comedies hit that milestone internationally, “Bad Teacher” ($114 million) and “Just Go With It” ($112 million), while the studio’s “Friends With Benefits” came close, grossing $95 million overseas. All three made more money overseas than domestically.

Looking ahead, 2012 is light on laffers; 2011 had eight R-rated comedies during the summer alone. But a few American comedies could break out, even with overseas auds.

Universal’s “American Reunion” — the fourth installment in the “American Pie” franchise — launches internationally throughout April and May, followed by Sony’s “Men in Black 3” and Universal’s foul-mouthed teddy bear laffer “Ted.”

On the franchise front, summer 2012 will offer up plenty of potential overseas hits, including Disney-Marvel’s “The Avengers,” Sony’s “The Amazing Spider-Man,” Universal’s “The Bourne Legacy” and WB’s “The Dark Knight Rises.”

Later in the year, Fox’s “Taken” sequel should help keep B.O. clicking internationally, as should Summit’s “Twilight” finale, “Breaking Dawn — Part 2” and Warner-New Line’s first “Hobbit” installment, “An Unexpected Journey.”