Shooting on the Avatar sequels will begin by next October, according to star Sam Worthington in an interview with an Australian radio station via Variety.  Of course, the sequels have already been delayed substantially; they were once scheduled to begin production Fall 2012 (see "Three 'Avatar' Sequels”). 

But in a sign that this may be the real thing, Worthington said that the scripts for all three sequels have been largely written by Cameron, and that a group of writers that Fox had previously announced as hired to work on the film (Josh Friedman, Rick Jaffa & Amanda Silver, and Shane Salerno) were just polishing. 

All three sequels will be shot at once, according to Worthington.  With a total of four films, the franchise will rack up some serious box office; the first film has topped $2.75 billion worldwide, a record.