According to the http://uk.faqs.ign.com/articles/620/620559p1.html, Oblivion had at the very least "60,000 lines of spoken dialogue". This statement was in late May 2005. Oblivion came out in March 2006, so it's very possible even more dialouge was added between that time. Some guy here on the forums said Oblivion's voice BSAs haad 77,000 lines of dialouge or something.
Fallout 3 had over 40,000 lines of dialouge: http://www.computerandvideogames.com/192438/news/bethesda-over-40000-lines-of-dialogue-in-fallout-3/
@Above: That's very strange it says 37,000 lines of dialouge. We got two very credible contradicting sources. Strange, who to believe?
I'll believe Mark Lampert who was the sound designer for the game. Especially when that interview with him was from 2007 and in it he says:
There are over 37,000 lines of spoken dialogue in Oblivion. Discuss."Yes, it would seem that our designers know no bounds when it comes to writing for our games. Also, consider this: at one point in development, there was almost twice that much! A figure was calculated and we knew that we could never fit that much into the game, so they all worked hard to hone it all down and still have it turn out so wonderfully."
So, at one point they probably did have 60,000. But like he said, they wouldn't have been able to make that work at the time.