Comic-book writer Steve Murphy of Mirage Studios has updated his Blog with a post that a sequel to this year's TMNT, may be in the works:

As of two weeks ago Imagi Entertainment (the TMNT movie animation studio) informed Mirage Studios that there was a 50-50 chance of a CGI film sequel. Last week they upped the odds to 70-30 in favor of a sequel, as talks between Imagi and their distribution partners Warner Brothers and the Weinstein Group seem to be heading in a positive direction....
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TMNT is the computer-animated Teenage Mutant Ninja Turtles movie that was released this year by Warner Bros.