Peak Blue DEF Diesel Exhaust Fluid 2.5 galBlueDEF Diesel Exhaust Fluid is a non toxic solution engineered to help diesel powered vehicles reduce emissions and improve fuel economy. Engineered for use in Selective Catalytic Reduction (SCR) systems on diesel engines, BlueDEF diesel exhaust fluid is comprised of a high purity synthetic urea and deionized water mixture that improves emissions and fuel economy. Mixture of 32. 5 percent high purity synthetic urea and 67. 5 percent deionized water