James Cameron's third 'Avatar' movie has big opening, but the weeks that follow could determine if parts 4 and 5 are ever made.

"Avatar: Fire and Ash," the third installment in James Cameron's blockbuster sci-fi fantasy series, debuted atop the North American box office with $88 million in ticket sales in the weekend before Christmas, industry estimates showed Sunday.

"Fire and Ash" grossed $345 million worldwide in its opening weekend, and is expected to do very well abroad, according to David A. Gross of Franchise Entertainment Research.

The "Avatar" films "connect everywhere around the world," Gross said, adding that the 20th Century movie -- like its predecessors -- would likely rev up on "outstanding word-of-mouth."

"The openings are not what the Avatar movies are about. It's what they do after they open," Gross said.

The movie once again stars Zoe Saldana and Sam Worthington as Na'vi warrior Neytiri and ex-Marine Jake Sully, who must battle a new foe threatening their family's life on Pandora.