Prestone Command(R) DEF is a safe, easy-to-handle nontoxic solution of 67.5% water and 32.5% automotive-grade urea. It is a stable fluid that is colorless and odorless. Prestone Command(R) DEF usage will vary by vehicle. Most OEMs estimate usage will be 2-3% of diesel-fuel consumption. On average, this amounts to one gallon of DEF to every 50-75 gallons of fuel. Check owner's manual for proper usage in your vehicle. DEF reacts with certain metals such as aluminum, copper and brass. Therefore, only place DEF in storage tanks and dispensing equipment made of stainless steel or high-density polyethylene.