from the Box Office Mojo article:
In a year that relied heavily on sequels and 3D, total domestic box office tumbled 3.8 percent to around $10.17 billion. That's the third-highest grossing year ever, though it ranks behind both 2009 and 2010. What's worse is that ticket sales fell roughly 4.7 percent to 1.28 billion, which is the lowest level since 1995.
Around $400 million separates 2011 from 2010, which can entirely be covered by Avatar's $478 million gross in 2010. Most of that was made in the first quarter, which contributed to the massive 21 percent first quarter downturn in 2011. From then on, the year was fairly solid—the second and third quarters set new records with $2.84 billion and $2.89 billion. Within those quarters, April, May, July and September were all record months, and July 2011 ranks as the highest-grossing month of all-time at $1.394 billion.
Business slowed down again by the fourth quarter, though, with receipts dropping five percent to $2.34 billion. That's troubling considering the abundance of seemingly proven franchise fare, especially in the last two months of the year. December in particular showed that sequels alone aren't going to do the trick: Sherlock Holmes: A Game of Shadows ($124.1 million), Mission: Impossible - Ghost Protocol ($122.3 million) and Alvin and the Chipmunks: Chipwrecked ($88.2 million) weren't strong enough to lead to a year-over-year improvement.