Diesel fuel prices in the U.S. continue to break all-time records, hitting $6.28 a gallon as a national average on Sept. 14, 2026, and they aren’t likely to come down anytime soon. Because diesel is the fuel for freight transportation, farming and construction – and is related to a key heating fuel – the effects are set to spread across the entire U.S. economy.

The inflation-adjusted price of diesel in late August was about as high as it was in 2022 and has likely risen further. There are still three factors that we, scholars of U.S. and global energy markets and supply chains, see that set the stage for prices to remain high and potentially climb even further.

Two of these elements – environmental protection regulations on oil refineries and Russia’s war with Ukraine – have been building tension for years. But the situation has been pushed into a crisis by the U.S. war against Iran, which has closed the Strait of Hormuz to a large percentage of oil and refined products shipments for more than six months.

Amid that crisis, U.S. oil refineries are making lots of money.

In mid-September 2026, diesel prices were up 67% over September 2025’s monthly national average of $3.75 a gallon, and they have risen sharply since. In January 2026, before the U.S. and Israel first attacked Iran in late February, the average diesel price in the U.S. was lower, at $3.52 a gallon – meaning that diesel prices have jumped more than 78% since the war began.

In part, that’s because the country, and the world, have been losing diesel refining capacity for many years and can’t just ramp up production to fill the shortages.

Refinery capacity........

© The Conversation