bk44 can be used in both gas and diesel, they sell a quart sized bottle for diesel but according to my local rep its mearly a larger bottle for larger tanks on diesel trucks, bg makes a product called diesel care, which is pump through a machine and run thourgh the motor like there gas version but none of my local dealers have the machine, the closest dealrer is 100 miles east of my town, in the event im traveling that way i'll schedule an appontiontment a try there product and get back with everybody on the results.