Until recently, it was believed that 50-ppm sulfur would be the main diesel specification. However, strong signs indicate that the European Community will drop sulfur specifications to 10 ppm. Equally important, other specifications, such as, PNA, density and cetane may also change. New, proposed U.S. legislation is focused on sulfur reductions. In December 2000, the U.S. EPA published mandates for 15-ppm sulfur diesel by 2006. Some major oil companies have adapted the policy to produce clean burning, so-called "green", fuels. Consequently, strong drivers do exist for further product quality improvement.