Natural Resources Defense Council. July 2014.
Large fuel purchasers are increasingly turning to biofuels to improve their environmental performance. These efforts are well intentioned but warrant caution. While biofuels can certainly provide environmental benefits, they can also cause severe damage if produced unsustainably, because biofuel feedstocks are inextricably linked to land, water, and wildlife. [Note: contains copyrighted material].
http://www.nrdc.org/energy/files/biofuels-sustainability-certification-report.pdf [PDF format, 98 pages].