It's notoriously hard to predict gas prices. Who would have thought in 2006 that we'd be paying $4 a gallon in 2008? Or, as prices peaked last year, that we'd be filling up for $2.50 a gallon this summer?
That said, civil engineer and Forbes reporter Chris Steiner argues that prices will rise precipitously over the next few decades. (It would probably make as much sense to argue that electric cars will take over and gas prices will fall, but that's another argument for another day.)