Host Stephanie Potter speaks with Andrew Nikiforuk, author of "Tar Sands: Dirty Oil and the Future of a Continent." Canada is the largest supplier of oil to the U.S. Canada now produces more oil than Texas or Saudi Arabia. Canadian tar sand oil is dirtier and more environmentally destructive than conventional oil.   In his recent book Tar Sands: Dirty Oil and the Future of a Continent, Nikiforuk critiques the oil industry, oil-friendly bureaucrats, and petrol-guzzling North Americans for contributing to the problem. (More links: GreenPeace Vacation spoof, Oil Sands Truth, Oil Sands Watch. )