The graph is from Peter Tertzakian who notes:
To put this in perspective, 1,000 Tcf of natural gas contains the equivalent energy to 166 billion barrels of oil – a staggering amount considering that the discovery of 10 billion barrels of conventional oil these days is a rare occurrence, worthy of many headlines…
Estimates of recoverable shale gas have doubled in just the past year and shale gas is only part of the supply with the total being 2,552 trillion cubic feet (Tcf) of potential natural gas resources in the U.S. alone. Per unit of electricity, burning natural gas results in significantly fewer carbon dioxide emissions than coal. It is possible, however, that fracking may leak more methane to the atmosphere so the net climate benefit is unclear, at least given current methods of development.
Hat tip: Paul Kedrosky.