At a recent stop at the Buc-ee's off I-40 at the Sevierville, Tennessee exit, I noticed the letters "DEF" over a few pumps, wondered what they meant, and found the answer interesting and a little gross. "DEF" stands for "Diesel Exhaust Fluid," and it's used in many diesel vehicles to reduce air pollution by lowering nitrogen oxides using a selective catalytic reduction (SCR) system that breaks down harmful nitrogen oxide emissions into harmless nitrogen and water. So far, so good, until I learned that DEF is a solution made of 32.5% urea and 67.5% deionized water. Yuk. In other words, not drinkable.
Buc-ee's sells DEF at those marked pumps for $3-4 dollars per gallon, or you can purchase pre-packaged jugs inside the store and save about 50 cents per gallon. Sure beats getting it at Amazon for several times the price. I'll never look at an 18-wheeler the same.
More information, in case you're oddly interested, can be found at the link below.



