The "Energy Information Administration" (I didn't even know that agency existed) lists average US highway diesel history/projections this way:
Diesel (dollars per gallon)
2017 $2.65
2018 $3.18
2019 $3.06
2020 $3.09
They attribute the slight increase in diesel to the International Maritime Organization (IMO) which is another one of those, who knew they even existed...
Who knows where 2021 and later prices will be ???
https://www.eia.gov/outlooks/steo/report/prices.php