In a recent interview, Pete Hines, Bethesda's president of public relations and marketing revealed that, depending on the player's actions, Fallout 3 will have up to 12 different endings.
Fallout 3 will be as open ended as Oblivion but in a different way, Hines explained. "One of the things about Fallout 3 is you cannot do everything in this game. It's not like Oblivion where it's just - basically, anybody could do anything. Fallout isn't like that", he said. "Fallout basically is fewer number of quests with lots of ways to complete them and things are opened up to you or locked off to you as you go through the game."
"There will be somewhere between nine to 12 different endings to the game based on what you've done in the game. So it's something that is inherently a diverging path. It may be some of the same things but doing them in very different ways, and ultimately that will define your gameplay experience."
"Then you'll have to go back and play again. So you may have to play through once and blow up Megaton [a major city in the game] and then play again and not blow up Megaton just to get to the bits that are all behind both of those paths."