Oil above $100 is a bet on how long Hormuz stays shut

Brent crude traded above $105 a barrel on September 10th, its highest since May, and the S&P 500 fell in sympathy. The cause was a war that was supposedly over. In June the United States and Iran signed a memorandum of understanding that envisaged reopening the Strait of Hormuz and bought a fragile truce. By early September both sides were striking tankers again, and oil was doing what it always does when the world's most important door appears shut: rising far faster than the physical barrel moving through it.

For the retail investor the number arrives three ways at once. It shows up at the petrol pump, in the margins of every company that ships things, and in the energy shares that have already rallied hard. The question is not whether a war with Iran is bad for oil prices — it plainly is. The question is how much of the rally is real, and how long it can last.

A chokepoint shot at from both sides

The Strait of Hormuz is the hinge of the whole story. Roughly a fifth of the world's oil normally transits that narrow passage between the Persian Gulf and the Gulf of Oman. In the ten days to September 7th, commodity-ship traffic through it had fallen to ten vessels a day, the lowest since May, according to data from Kpler, a research firm. The United States says it struck three Iranian oil tankers, one near the country's main export terminal at Kharg Island; Iran's Revolutionary Guards say they hit six ships in retaliation. When both sides are shooting at tankers in a strait that carries 15-20m barrels a day, every barrel that still finds a route across is worth more. That is the mechanics behind the headline.

The natural experiment in a risk premium

The striking thing is not that oil is up, but how much of the gain is politics rather than physical shortage. Oil traded near $60 at the start of 2026, spiked to almost $140 when America, Israel and Iran went to war in late February, then cooled — losing roughly half its war gain — as the June truce took hold. The instructive detail is that the rally's retreat happened while the strait never fully reopened: Iran kept charging ships million-dollar tolls, continued limiting crossings, and US naval forces still had to clear mines. Prices fell for the same reason that the market now lets them surge. Barrel for barrel, not much had changed. What changed was the expectation of whether the conflict would end.

That is what a war premium is: a bet on a political outcome, resting on top of the physical price of a barrel. Buyers are not paying $105 because there is suddenly a deficit of crude in storage. They are paying it because they are no longer certain the strait stays open. And that uncertainty can reverse as abruptly as it was created — as June showed.

The buffers are drawn down

The trouble is that the institutions built to absorb such a spike are now in their weakest shape in decades. America's Strategic Petroleum Reserve, the emergency cushion drawn on since the early 1980s, has fallen below 300m barrels for the first time since it was filled; the war has already released 172m barrels, and engineers caution that pumping slows and the caverns lose structural integrity below this level. OPEC's spare capacity, the other great stabiliser, is largely captive to the same chokepoint it would have to bypass. Saudi Arabia's East-West pipeline, the main route that dodges Hormuz, is running flat out at its full 7m barrels a day of capacity, leaving almost no headroom; at full tilt it still covers only about 85% of the kingdom's typical exports. The Emirates' alternative route will not be doubled until 2027 — too late to matter now.

Which is why the loudest forecasts are conditional, not guaranteed. Goldman Sachs has warned that Brent could push past $120 a barrel — but the bank attaches a condition: Gulf output must remain roughly 4m barrels a day below pre-war levels into 2027. The US Energy Information Administration, by contrast, expects Middle East production to rise as the strait gradually reopens. The difference between those two outcomes is not geology. It is politics.

What it means for energy investors

For anyone tempted to chase the rally, the calendar is a warning. ExxonMobil is up roughly 40% this year, to about $165, with Brent near $100 lifting its second-quarter earnings to $14.5bn; Chevron and the XLE energy ETF have done better, up 44% and 48%. Those numbers show the leverage: energy earnings scale almost directly with the price of oil. But they also show how much has already been priced in. With oil at $105 carrying a fat political premium, a chunk of those gains rests on the war lasting. In June it vanished in a matter of weeks.

The honest framing is uncomfortable but useful. Buying energy on the back of a closed strait is not a wager on physics or on the economy. It is a wager on how long a conflict lasts — a variable that governments, not barrel counts, control. The upside comes to whoever holds energy if the war drags; the downside is the premium deflating as quickly as it appeared, dragging the shares with it. That asymmetry is the real risk in the rally, and it is worth more thought than the price at the pump.