O IL TRADERS are inherently strong-stomached, but even for them October has been a woozy month. On October 3rd the price of Brent crude reached $86 a barrel, a four-year high. On October 23rd it slid to $76, on the news that demand might ebb, stockpiles rise and production increase. At the centre of this is Saudi Arabia, the world’s most powerful petrostate. Khalid al-Falih, the country’s oil minister, said on October 23rd that the kingdom was prepared “to meet any demand that materialises”. But that is not an easy task.

Exports from Iran have plunged and are due to fall further after November 4th, when new American sanctions take effect. Even as America’s crude production soars, President Donald Trump has demanded that the Organisation of Petroleum Exporting Countries (OPEC) boost output to lower prices. Saudi Arabia seems keen to appease him, both because it supports the sanctions and because of anger over the killing of Jamal Khashoggi, a journalist, in the Saudi consulate in Istanbul. But the gains from producing more are uncertain. Both OPEC and the International Energy Agency (IEA) have cut their forecasts for oil demand in 2019.

Even if Saudi Arabia wants to fill the gap left by Iran, it is not clear that it can. That is in part because Saudi output is already so high. As Iranian exports have dropped since May, when Mr Trump announced the sanctions, Saudi Arabian exports have picked up. The kingdom is producing more than 10.5m barrels of oil a day (b/d); officials claim the capacity to produce around 12m. “They can reach about 11m barrels with relative ease,” explains Neil Atkinson, head of oil markets at the IEA. Analysts debate how quickly—or whether—the country can ramp up to 12m b/d. “They have never actually proven they can do that,” says Ehsan Khoman of MUFG, a bank.

Saudi Arabia may also be unable to counter weakness in smaller petrostates, where supply could drop unexpectedly. In the past six months Nigeria, Libya and Venezuela have helped to offset falling exports from Iran. But they are a volatile trio.