The benchmark diesel price used to calculate most fuel surcharges reached a significant milestone this week, climbing to its highest level since military action against Iran began in early March.

The Department of Energy/Energy Information Administration (DOE/EIA) average weekly retail diesel price rose 19.8 cents per gallon to $5.652/g, effective Monday and published Tuesday. The move surpassed the previous high of $5.643/g set on April 6. Over the past two weeks, the benchmark has now gained 39.5 cts/g.

The retail strength reflects recent activity in futures markets. Ultra low sulfur diesel (ULSD) on the CME commodity exchange had increased in 12 out of 13 trading days through Friday, a run that translated into the higher retail price published by DOE/EIA. Because the benchmark is a weekly average of retail pump prices rather than a spot quote, futures moves reach it only with a delay, and any sustained reversal would take time to register as well. On Monday, however, ULSD reversed course, declining 22.72 cts/g to $4.2677/g. By approximately 10 a.m. Monday the contract was up slightly, though it had been down about 6 cts/g earlier in the session.

The high settlement during that run-up came on Friday, when ULSD settled just under $4.50/g, moving closer to the March 20 settlement of $4.6084/g — the highest settle since military action against Iran began.

The sudden downward turn in prices, which began as soon as trading on the CME commenced for the week Sunday evening U.S. time, has been attributed to U.S. Treasury Secretary Scott Bessent saying the Trump administration will focus more on economic pressure on Iran rather than renewed military action.

The diesel market has been marked in recent weeks by strengthening at the retail level, even as retail gasoline has not moved anywhere near as much. The AAA average daily gasoline price on Tuesday was $4.0969/g; a month ago it was $4.1109/g. Retail diesel, according to AAA, was $5.2778/g a month ago and stood at $5.6199/g on Tuesday.

Diesel markets have their own set of bullish factors that gasoline avoids: Ukrainian strikes on diesel-oriented Russian refineries; the physical qualities of Middle East crudes that are not getting to market, which tend to produce high quantities of diesel; and, as has been the case for several years, reduced demand for the marginal barrel of gasoline because of steady adoption of electric vehicles around the world, though less so in the U.S.

A debate that has been ongoing in oil markets over the last several days centers on wide swings in estimates of the amount of oil getting through the Strait of Hormuz. Before the war, the strait routinely moved about 20 million b/d — roughly a fifth of global oil consumption — so those flow estimates carry broad significance for world supply.

Much of the discussion was spurred by reporting from Axios, which quoted unidentified U.S. officials as saying a "stealth" transit led by the U.S. through the southern portion of the Gulf, aimed at avoiding Iranian attacks, has helped the supply of oil out of the Gulf get up to 10 million b/d — still only about half of the pre-war level. Because that information came from Trump administration officials, the number received significant pushback on social media.

David Wech, chief economist at tanker-tracking firm Vortexa, told CNBC on Friday that the number the firm sees fluctuates. While he did not refer to the Axios report directly, he indicated it could be accurate on some days.

"Currently, where we are seeing it depends a lot on which time period you look at," Wech said. "On the average of the last month, we see six to seven million barrels per day of crude oil going through. There are peaks in our data on the seven-day moving average of up to close to 10 million barrels per day, and the best day we saw was 40 million barrels per day. So it depends really a lot what time period you're looking at."

The next weekly DOE/EIA publication will show whether Monday's futures reversal begins to feed through to the retail benchmark, or whether the two-week, 39.5 cts/g climb at the pump holds.

John Kingston reported this story for FreightWaves.