In January 2007, California adopted a Low-Carbon Fuel Standard (LCFS) that requires a 10 percent decrease in the carbon intensity of California's transportation fuels by 2020.
Source: The California Energy Commission

Under the LCFS, fuel providers are required to track the life cycle global warming intensity (GWI) of their products, measured on a per-unit-energy basis, and reduce this value over time. This first-in-the-world greenhouse gas (GHG) standard for transportation fuels will spark research in alternatives to oil and reduce GHG emissions.