Titanic made 50% more money after ten weeks Avatar does not have quite the legs of Titanic but it is close. 30% more box office is possible, especially in foreign markets where a good performing movie is often not squeezed out of theatres as quickly as in the US.
$3.06 billion would be Avatar total if there is another 20% of box office
$3.3 billion would the world box office total for Avatar with another 30% box office.
$3.55 billion total if there is another 40% box office.
$3.8 billion if there is another 50% box office.
My new prediction (guestimate) is $3.3 billion world box office which would be almost double the old non-inflation adjusted record for Titanic. Double would be $3.6 billion in world box office.