In 2008, the Washington State Legislature established a goal to reduce state greenhouse gas emissions to 1990 levels by 2020 with additional goals for 2035 and 2050. Since the transportation sector is responsible for almost half of the state’s greenhouse gas (GHG) emissions, reductions from vehicles and fuels are fundamental to achieving the state goals. In May 2009, Washington’s governor directed the Department of Ecology to assess whether a clean fuel standard would best meet Washington’s GHG emission reduction goals. The objective of a clean fuel standard is to reduce the overall carbon intensity of transportation fuels where carbon intensity is defined as the direct well-to -wheel (WTW) GHG emissions and any indirect emissions from land use change per unit energy. A bounding scenario analysis was performed to quantify fuel types and volumes needed for compliance, changes in consumer spending on vehicles and fuel, infrastructure costs, and the corresponding macro-economic impacts. The study concluded that volumes of alternative fuels would increase, petroleum consumption would decrease, state-level GHG emissions from transportation (as captured by assumed carbon intensity ratings and volumes) would decrease, and there would be a small (in most scenarios positive) impact on the state economy relative to the business-as-usual projection.