The pileup was created in part because studios want to capture some of the excitement surrounding "Avatar," the James Cameron epic released in December. At $2.4 billion in global ticket sales, it is the highest-grossing film ever. In addition to the novelty or richer experience that might drive more people to see a 3-D movie, tickets to 3-D movies also cost a few dollars more. Around the time "Avatar" came out, Warner Bros. decided to convert a remake of "Clash of the Titans" from 2-D to 3-D and push its release back a week, to April 2. That will be the third 3-D movie to hit the market in a short span. DreamWorks Animation SKG Inc.'s "How to Train Your Dragon" comes out a week earlier, and The Walt Disney Co.'s "Alice in Wonderland" hits theaters March 5. And "Avatar" might still be playing in some places too. But a limited number of theaters can show these movies in 3-D, because not all theater owners have bought new digital projectors and undertaken other upgrades necessary to show movies in the format. About 3,900 to 4,000 3-D-ready screens are expected to be available in the U.S. and Canada by the end of March. Typically a movie in wide release might be shown on 3,000 to 10,000 screens in North America. In the past, a smaller number of 3-D-capable screens was adequate when one major film at a time was being released in 3-D in addition to 2-D. Each movie had a longer run, and moviegoers who wanted to see it in 3-D could pick a convenient time to go. With three out at once, each will get less exposure because some theaters with only one or two 3-D screens will have to choose which movies to show in 3-D. "One or all three are going to suffer in some way," said Patrick Corcoran, director of media and research for the National Association of Theatre Owners. "It makes it a much harder decision on exhibitors on what to keep or what to drop or what to add and probably should have been avoided."