The spread draws a border: the Hormuz disruption is now priced outside the US, and Brent-linked importers pay for the $11.91 gap

$3.94 in a week: the price split between two shores

According to Investing.com historical tables, ICE Brent futures closed at $100.34 on 21 September and $104.32 on 25 September; over the same days WTI moved from $92.37 to $92.41. The Brent–WTI spread was $7.97, $8.73, $10.92, $11.99 and $11.91 respectively, widening by $3.94, or about 49%, in five sessions. According to Reuters' analysis of 25 September, WTI fell intraday to $12.02 below Brent on 24 September, the widest discount since 6 May, and the spread has not returned below $4 since 7 July. In Cornerstone Futures' morning note of 25 September, the spread between the November contracts was measured as wide as $12.83.

Physical flows through Hormuz did not improve in the same week. According to Straits.live's summary of 26 September, IMF PortWatch recorded only 1 transit for 20 September, against a pre-crisis average of 85 a day, and 313 ships with AIS switched on were waiting in the monitoring box. On 26 September US President Trump rejected Iran's 7-day reopening plan, which Iran had tied to the lifting of the blockade, an oil sanctions waiver and about 12 billion dollars in frozen assets; according to CBS News, the US military escorted about 40 million barrels in 48 hours and the blockade has turned back 122 ships in total. Brent fell 2.1% on 25 September on diplomatic hopes but closed the week higher; what pulled WTI down was not Hormuz but America's own domestic calculus.

Anatomy of the spread: $8 of freight, the rest a diesel wall

The hidden link is this: the spread prices not that US crude has become cheap for the world, but that it cannot reach the world. As reported by Reuters, Bob Yawger of Mizuho said the WTI discount needed to cover freight costs used to be about $4 and is now about $8. The cost of a VLCC from the Gulf Coast to Asia has risen from $16 million before the war to about $50 million; for a ship carrying about 2 million barrels, by our calculation, that means a rise from $8 to around $25 per barrel, which on its own exceeds the $11.91 spread. This is why US crude exports rose by only 45 thousand barrels a day from July to August, to 3.72 million barrels, and in September are falling for a third consecutive month towards their lowest level since before the war.

Diesel explains the remaining $4 or so. Trump said on 22 September that he supported a diesel export ban, the White House denied reports the next day that it was preparing a 90-day ban, and Energy Secretary Chris Wright argued that a ban would not bring prices under control. According to Wood Mackenzie, a ban would mean about 700 thousand barrels a day of diesel heading into storage and refineries cutting runs by 12%, or more than 2 million barrels a day; Morgan Stanley calculates that the US produces 5.1 million barrels a day of diesel and exports 1.2 million barrels of it. Less crude to be processed pushes the price down at Cushing: according to DTN, the WTI front month and ULSD futures fell more than 7.5% and 8% respectively over the week, while at the pump US diesel hit a record 6.528 dollars a gallon.

Why the disruption piles up in the east

Together these two walls draw a border that partly insulates the US from the price effect of the disruption: crude can be processed in abundance at home and product exports can be curtailed, while barrels heading abroad are expensive because of freight. The result is that the cost of Hormuz remaining closed collects east of the Atlantic and in Asia, among buyers linked to Brent and Dubai. According to Petroleum Economist's August–September issue, the Brent–Dubai EFS spread, below $2 before the crisis, swung between $3.05 and $16.25 in June–July; according to the same piece, geography is now more decisive than crude grade. In June a record 3.5 million barrels a day of crude went from the US to Asia, with Japan alone taking 530 thousand barrels a day; at September's freight levels that flow becomes hard to sustain.

The EIA's short-term outlook published on 9 September projected Brent averaging around $90 in the second half of 2026; the 25 September close is $14 above that assumption. The same report says US distillate stocks will fall below 100 million barrels in September and remain below the five-year low for most of 2027. This shows that the diesel export ban debate is not passing political rhetoric but pressure fed by inventory data: the more the US keeps distillate at home, the wider the product deficit in Europe and the Mediterranean grows.

Türkiye: the US barrel arrived, its discount did not

Türkiye was not caught unprepared by this shift; on the contrary, it diversified its sources. According to a 29 August report in Cumhuriyet based on EPDK data, no crude was bought from the US in January–April, yet the US share rose to 13% in May and to 21%, or 570,676 tonnes, in June, putting the US ahead of Russia in first place. But this barrel reaches Türkiye not at the WTI price but with freight added and delivered to the Mediterranean, that is, on a Brent basis; the $8 freight threshold means that most of the spread never reaches the Turkish buyer. By our calculation, at the 25 September rate of 48.97 dollar/TL, the $11.91 gap is worth about 583 TL per barrel and about 3.67 TL per litre; this is the invisible premium Türkiye pays because of its geography.

At the pump the link is more direct. Under EPDK rules, the ex-refinery price before duties is formed by tracking CIF Mediterranean product prices at Genoa–Lavera and the daily dollar rate; in other words, diesel is tied not to crude at Cushing but to the diesel price in Europe. Diesel exceeded 100 TL in Türkiye for the first time on 17 September, fell by 5.50 TL to 90.90 TL on Istanbul's European side on 24 September, and returned to 93.45 TL after a 2.55 TL increase on 25 September. With Russia extending its diesel export ban to 31 October, Türkiye was already squeezed on product supply; the same Cumhuriyet report lists the US as the third diesel supplier after India and Italy, although the text does not make clear which month that ranking refers to. A US diesel ban would close one of Türkiye's two large alternative sources in the same autumn.

The bill is therefore written not from the cheapening end of crude but from its expensive end. Türkiye's energy imports rose 13.1% in July to 5.826 billion dollars, and 7.2% in January–July to 40.086 billion dollars; in June the increase was 28.8%. Ember's analysis of 12 June estimated that the Hormuz crisis would add about 14 billion dollars to the bill by the end of 2026, 7.7 billion of it from oil, and that road transport would account for about a third of the bill; that calculation was made before September, when diesel passed 100 TL.

What to watch and uncertainties

Three indicators will test this reading. A durable fall of the spread below $10 would indicate that freight has eased or that the risk of a diesel ban has faded. Daily Hormuz transits exceeding 20 would be the first physical sign that the geographic premium in Brent is starting to melt. Brent futures breaking above the intraday high of $108.23 on 24 September would signal that the cost of the disruption in the east is growing and that diesel is heading back towards 100 TL.

The uncertainties are quantified too: WTI's weekly loss is 7.5% at DTN and about 4.5% in the Investing.com table; the difference may stem from the contract roll. Estimates of crude flows through Hormuz range from 3.7 million to 16.4 million barrels a day, and Trump's claim of 29 ships could not be verified by independent counts. The per-barrel VLCC cost was calculated by us on the assumption of a full 2-million-barrel cargo. As of tonight, Türkiye's August energy bill has not been published in detail, and the pricing formula under which Turkish refineries buy US crude could not be verified.