The federal government estimates that there's more than 1 trillion barrels of burnable fuel in the oil shale of the Rocky Mountains.

NPR: Industry Seeks to Extract Oil from Rocky Mountain Shale

We also have huge land and offshore oil reserves vital for transportation fuel, including enormous amounts contained along with gas in oil shale deposits amounting to several hundred years of supply.

FORBES: Renewable Energy Delusions: Getting A Real Grip On Alternatives

Oil shale and tar sands are other sources of liquid fuel that are harder on the environment than petroleum.

NPR: Will Pricey Fuel Prompt Greener Energy Habits?