In this MTV interview James Cameron is not only letting everyone know that there is a 2 and 3 but a 4th installment of Avatar that would be a prequel to the first film. It would cover what went wrong with the humans and the locals. Avatar 2 for your info will be released sometime in 2015 but I am assuming since the script of 2 and 3 is being written as one that the filming will also be shot back to back much like the last Harry Potter film was. Which means the release date for the 3rd installment will be more closer to a year or earlier later. That is assuming they shoot it back to back.