All eyes on Saudis as Iran curbs take effect

However, oil prices have fallen by nearly $15 in less than a month, after peaking in early October at their highest level in two and a half years, with a barrel of Brent at over $85.

Part of the explanation lies in the ambiguous position of the US, which initially insisted that the sanctions were designed to reduce Iranian exports to zero barrels, but has since has softened its position.

Secretary of State Mike Pompeo on Friday announced exemptions for eight countries, without naming them. Turkey indicated that it was one of them and analysts believe that India, one of the world's largest importers, is also on the list, which will be published on Monday. "India said to the US that they can't stop before March, they are facing a major currency crisis," explained Joel Hancock, analyst at Natixis.

Consumer confidence in the US itself could also suffer if rising oil prices translate into higher prices at the pump. "If prices start to rise again or another major producer has difficulties, it could put pressure on the US and lead to new exemptions," said Fabiani.

The other major oil producing countries are expected to ramp up production to try and compensate for Iran's anticipated decline in output. But in doing so, they run the risk of hampering their ability to react to any future crises.