ENERGY SOURCE	EQUIVALENT BARRELS OF OIL (in billions)	PROS & CONS

TAR SANDS	175	
Large North American reserves	
Refining requires large amounts of water and natural gas and is destructive to local landscape


NATURAL GAS	1,058	
Fewer greenhouse-gas emissions than other fossil fuels	
High pressure makes it dangerous to transport and handle

OIL SHALE	2,600	
Abundant in the United States	
Extraction process is still experimental and produces a lot of waste rock


COAL	3,974	
Large reserves in energy-hungry countries like China and the United States	
Conversion to a liquid fuel is less cost-effective than just burning it to produce electricity

BIOMASS	RENEWABLE	?
The only combustion fuel that might reverse climate change	
Ramping up production may require competing with food needs for agricultural resources


Source: BP Statistical Review of World Energy; Cambridge Energy Research Associates; Chevron; U.S. Department of Energy, 2006