Factual error: The evil man request 100,000 pieces of gold for ransom. Each gold piece looks to be about 10 ounces, and 100,000 of those would make the entire thing weigh about 31 tons, but 2 guys are carrying it around in a little chest throughout the movie.
Continuity mistake: In the trailer, there is a scene showing Matt Damon in a fight. The other person pulls out a knife and cuts Damon on the right side of his face, leaving a big scar. In the next scene of the same commercial the scar changes from the right side of his face to the left side and then back again.