Photo from first Avatar (2009)

"The filmmaker announced that there will be four Avatar sequels, not the previously planned three. "We have decided to embark on a truly massive cinematic process," he said.

Cameron said as he was planning the three sequels, he found it limiting. "We began to bump up against the limitations for our art form," he said, explaining that he decided he would need more installments to tell the whole story.

Cameron said each of the four sequels will be able to stand alone, but will together create a saga. His goal is to release Avatar 2 at Christmas 2018 and then a new film in 2020, 2022 and 2023."

- Hollywod Reporter

To read the full story please go here . I think it's safe to assume all these movies will be in 3D , considering that the first Avatar is most famous for having fantastic 3D.

Source: Hollywood Reporter