James Cameron's "Avatar" is on a course to sink "Titanic" at the box office. No. 1 for the sixth-straight weekend with $36 million, the 20th Century Fox sci-fi spectacle lifted its domestic total to $552.8 million, according to studio estimates Sunday. "Avatar" raised its worldwide total to $1.841 billion. That's $2 million shy of first place behind Cameron's last movie, the 1997 shipwreck epic "Titanic," at $1.843 billion.