The “crack spread” is the ratio of gasoline to diesel when you send a barrel of crude oil through a refinery. You typically get twice as much gasoline than diesel, but that varies with the quality of the crude oil.
It’s within Iran’s power to give us $15/gal diesel on the West Coast if they want to punish Trump and Netanyahu to the max.
{{ The world isn’t running out of oil. It is running out of places to turn that oil into fuel. Which means the price of refined products such as gasoline will remain high. }}
Where it gets tricky, is when a distillate like diesel is in short supply. You would have to make more gasoline to get the diesel you want, but that reduces gasoline prices. So the refiner is going to charge you even more for the diesel.
US West Coast gets most of it’s refined products from the Middle East.