I see in The Hill that some critics of shale gas drilling are pointing to a revised estimate of the shale gas resources in the Marcellus formation as evidence that there's not enough gas to justify any risk from hydraulic fracturing. Earlier this week the US Geological Survey updated its previous estimate to 84 trillion cubic feet (TCF) of natural gas, a figure substantially less than the estimate of 410 TCF from the Department of Energy. Now, I'd have thought that even without doing the math on this, 84 TCF would still sound like a heck of a lot of gas, even if trillions have become the new billions in another context.

Perhaps cubic feet of gas don't convey quite the same degree of familiarity as barrels of oil, which most people can visualize, so it might be useful to think of this gas in its oil-equivalent terms. Using standard conversion factors, that 84 TCF in the Marcellus equates to roughly 14.5 billion barrels of oil. For comparison, that's half again as big as the original estimate of 9.6 billion barrels for the Prudhoe Bay field on the Alaskan North Slope. (FYI, Prudhoe Bay had produced a cumulative 11.5 billion barrels as of the end of 2007 and was still estimated to have a few billion barrels to go.) In that light, does anyone still want to argue that the Marcellus resource is inconsequential?