Check out the stats
1. Titanic $1,842,879,955
2. Return of the King $1,119,110,941
3. Dead Man's Chest $1,066,179,725
4. Avatar $1,063,151,759
5. The Dark Knight $1,001,921,825
http://boxofficemojo.com/alltime/world/
Although ticket prices have gone up & also imax tickets are way more expensive.
This will be #1 in no time
(note: titanic was on theaters for 41weeks!)