So what is your take on diesel fuel prices after 2020?

Unless producers of heavy/sour oil receive a higher price for their product (currently heavy/sour oil is sold per bbl cheaper(much cheaper almost 1/2 price) then WTI, hence why some refineries use the cheaper oil to offset costs of refining) Most refineries are set up to process WTI and/or heavy/sour crude... so world crude oil markets will determine the price, not the cost of processing.