Diesel and gasoline both come from the same barrel of crude oil. Typically, a refinery produces about 20 gallons of gasoline and 12 gallons of diesel from a 42 gallon barrel of crude, among other products.
So if demand for diesel jumps, they will make more of it, and the cost of both will rise accordingly.
So if demand for diesel jumps, they will make more of it, and the cost of both will rise accordingly.