PEAK Blue Def Diesel Exhaust Fluid 2.5 Gallons. Used in selective catalytic reduction systems on diesel engines to convert NOx to harmless nitrogen and water. A stable, colorless, non-flammable, non-toxic mixture of 32.5% high purity synthetic urea and 67.5% deionized water. Classified as minimum risk for transportation. Conforms to the ISO-22241-1 specification for def. API registered and meets or exceeds OEM specifications.