DEF* and that's all Halliburton runs at our camp is the new 6.7 and it's actually a hoss and handles all the abuse we give it and people def drive it like they are not theirs lol we have had a couple problems with the filters getting broken on lease roads but that was probably due to the. People that were driving them, if it means anything some of the most die hard cummins guys from work have traded in and grabbed a new powerstroke, I like them and feel like they are the best of the big 3 right now....