Truckers: Fill up your tanks immediately, if you have storage capacity, fill that too, and potentially even work with a broker to hedge against a "runaway market" in diesel prices coming in the wake of the U.S. and Israel's strikes against Iran.
That's what two pro oil market analysts said on Tuesday as diesel futures shot up about 80 cents in two days.
"It's pretty rare when history gets made this quickly," said Tom Kloza, chief oil analyst at Gulf Oil.
"We got a wholesale increase of 80 cents in two days," he said, adding that a big move like that isn't something refiners or truck stops will try to shelter customers from, and instead he expects prices at the pump to "move right away."
Tuesday at the Love's at I-65 on Trinity Lane in Nashville, the cash diesel price had already moved to $4.18/gal., credit another 6 cents higher. Down the street at a small service station you'd play hell getting a tractor-trailer into or out of, pricing remained in the $3.70/gal. range.
The last time a market shock happened like this was in 2022, when Russia invaded Ukraine. That invasion kicked off in late February and sent on-highway diesel prices rocketing up to nearly $5.80 a gallon.
Prices settled fairly quickly after that initial shock, but the war with Iran, specifically the threat to the Strait of Hormuz, a critical waterway that sees about 20 million barrels of crude oil and more refined products pass through a year, could send them flying up again.
"Iran hasn’t closed" the strait, said Kloza, but has attacked ships attempting to transit it. The result is that "the ship owners' insurance companies will not underwrite a trip under there" now. "That's going to change," one way or another.
[Related: Why is diesel getting so much more expensive than gasoline?]
Just when and how will mean a lot for diesel prices. 
Most of Iran's domestic-produced crude flows to China, but its situation on the Persian Gulf means it can pose a heavy threat to oil shipping lanes, which supply much of Europe and the North Atlantic.Wikipedia
The U.S. military has said it's sunk almost all of Iran's navy by now, but Iran has methods to fire on ships from land in the narrow pass, too.
On Tuesday afternoon, President Donald Trump said the U.S. would step in to guarantee the safe passage of ships through the narrow strait with the full might of the U.S. Navy.
“I have ordered the United States Development Finance Corporation to provide, at a very reasonable price, political risk insurance and guarantees for the Financial Security of ALL Maritime Trade, especially Energy, traveling through the gulf," Trump wrote on social media. “If necessary, the United States Navy will begin escorting tankers through the Strait of Hormuz as soon as possible."
Tracy Shuchart, CEO and Founder of Hilltower Resource Advisors LLC, said that coming out of a cold winter, the U.S. already had a diesel crunch.
"Diesel is literally ripping above 10% today," she said, looking at the chart for diesel futures prices on Tuesday morning. "We could see much higher diesel prices," even up to $4.50/gal. as an average. "I would not be shocked about that at all."
Kloza said it was a "no-brainer" today to "fill up your tank as soon as possible. Prices going up in what you’d describe as astronomic fashion," whether it's winter diesel, renewable diesel, or traditional.
Both Shuchart and Kloza expressed concern about Iran doing further damage to refineries in the region.
"I’m still worried that Iran could target more refineries and particularly refineries in the Persian Gulf," said Kloza. "One thing we learned in Russia fighting Ukraine is that you can disrupt billion-dollar properties like refineries with drones that cost $10,000."
Already, liquid-natural-gas capacity has taken a major hit, as the world's largest refinery of that fuel, Ras Laffan, was hit by Iranian forces. LNG is often used as a heating oil, but when prices get too high, it sometimes competes with diesel feedstocks.
Both Shuchart and Kloza called diesel a global commodity -- price increases in other markets often lead to price increases at home.
"When looking at energy prices, it’s useful to think about crude and diesel as truly global commodities," said Kloza. "Price increases for crude oil on other continents typically translate into similar increases for North American crude oil blends. Similarly, a 25 cents/gal. hike in European or Asian diesel will tend to support similar increases in the U.S."
In Nashville, Tennessee, Tuesday, Overdrive Editor Todd Dills already spotted evidence of diesel soaring past the $4/gallon mark -- last week's national average for diesel in the region was in the $3.60-$3.80 range, depending on where you filled up.
"Fill up now, or get a broker and start hedging your diesel costs now," said Shuchart.
How might an 80-cent cost swing hit your profit? Use Overdrive's Load Profit Analyzer to see it clearly.
[Related: What's an extra mpg worth in profit at today's freight rates? An extra 3 mpg?]
