Blue Def, 2.5 Gallon, Diesel Exhaust Fluid, Stable, Colorless, Non-Flammable, Non-Toxic, A Mixture Of 32.5% High Purity Synthetic Urea & 67.5% Deionized Water That Is Used Is Selective Catalytic Reduction Systems On Diesel Engines, Def Is The Primary Ingredient Used To Help Convert Nox To Harmless Nitrogen & Water, Classified As Minimum Risk For Transportation, Conforms To The ISO-22241-1 Specification For Def, API Registered & Meets Or Exceeds OEM Specifications.