Prestone HD1001 Command Diesel Exhaust Fluid - 2.5 Gallon Formulated to work with all SCR-equipped diesel engines Safe, easy-to-handle, nontoxic solution of 67.5% water and 32.5% automotive grade urea Certified to meet all API & ISO 22241 requirements Compatible with AdBlue and other DEF products DEF is a consumable and essential fluid for maintaining SCR-equipped modern diesel engines