Fox stepped on all the circulating rumors regarding James Cameron’s Avatar run time by releasing the official final cut’s duration down to the second.
James Cameron’s Avatar’s run time will be 161 minutes and 34 seconds, or 2 hours and 40-and-a-half minutes.
When rumors first began to spread about how long Avatar would run the times were in excess of three hours. Then they began to shrink down towards the two hour mark with the final number falling in the middle.
Featurettes like this one narrated by Sigourney Weaver suggest to me that James Cameron has a large cache of additional footage not crucial to the plot that was cut to maximize showings per day. The eventual 2010 release of Avatar on Blu-ray Disc and DVD will hopefully bring that footage home.