From an interview in 2006 (video below):

Everything that distinguishes our era from the dark ages is what we’ve been able to do with petroleum … and that is going to end very soon.

I think in the next few years we’re going to see the price of fossil fuels go through the roof, and there will be no substitutes for gasoline.

I think that, from my reading of history, the only fun most human beings have ever had - any feeling of power and respect - has been driving automobiles, you get in a car and everyone respects you; and people aren’t going to give that up easily.