Post Carbon Fellow David Hughes report for PCI Drilling Deeper was referenced in this article on the future of shale gas.

From the article:

The analysis echoes work by other researchers, including J. David Hughes, a geoscientist and research fellow at the Post Carbon Institute, a sustainability think tank based in California. In October, Hughes published a 300-page analysis, titled “Drilling Deeper,” which concluded that shale gas — as well as shale oil — is “unsustainable in the medium- and longer-term at the rates forecast by the EIA, which are extremely optimistic.”