A number of states are considering a Low Carbon Fuel Standard (LCFS) following California's adoption of its own standard earlier this year. An LCFS regulates the carbon intensity of transport fuels. It reaches as far upstream into the fuel supply chain as possible and focuses on the relatively small number of oil refiners and importers. Each company works under the constraint of a maximum carbon intensity (g of CO2e per MJ of fuel energy). This cap declines annually in order to reduce total emissions, and allows trading of emission credits between oil refiners, biofuel producers and electric utilities. Adding the right biofuels to the mix could reduce a suppliers average carbon intensity. This, of course requires a full life-cycle assessment of each fuel (well to tank + tank to wheels, including challenging issues such as co-product allocation and indirect land-use changes) in order to establish its carbon intensity. This is the first public policy initiative that codifies life-cycle assessment principles into law! More in an excellent article by Sperling and Yeh in Issues in Science and Technology.