Everyone knew that summer 2012 was going to be a big summer for superhero movies, but it's hard to imagine anyone could have predicted just how big it has wound up being. In a summer where blockbuster after blockbuster came up short, superhero movies turned out to be the only sure-fire winners of the summer With the summer movie season quickly winding down, it's virtually certain that comic book movies will finish with the top three spots at the summer box office in the United States. The Avengers is already a lock for first place with $616 million. The Dark Knight Rises has also wrapped up second place with $354 million and counting. And The Amazing Spider-Man looks to have a solid hold on third place with $250 million. With only four weekends left to go in the summer box office season, it's unlikely that even Arnold Schwarzenegger and Sylvester Stallone combined would be strong enough to knock a superhero out of the top three (even though they look to give it the old college try with The Expendables 2). Considering the first Expendables barely crossed the $100 million mark though, it's doubtful that Spider-Man is sweating the thought much. Here's what is even more amazing about the dominance of superhero movies in the summer of 2012. As of this past weekend, the total 2012 U.S. summer box office stands at $3.3 billion according to Box Office Mojo. Guess how much of that $3.3 billion was generated by the top three superhero movies? The Avengers, The Dark Knight Rises, and The Amazing Spider-Man have racked up a combined $1.2 billion at the U.S. box office so far this summer. This means that superhero movies have accounted for over 36% of the total 2012 U.S. box office. When was the last time any one genre of movie accounted for over one third of a total seasonal box office? We're not sure if it has ever happened before. Of course, it just might happen again next year, as Iron Man 3, Man Of Steel, and The Wolverine look to be three of the most anticipated movies of summer 2013.