Imagine a world in recession, where oil costs $50 per barrel. Which economies would be most affected? There are obvious losers. In Saudi Arabia, the largest oil producer, oil accounts for 90 per cent of exports, which in turn represents almost two-thirds of the economy’s output.

Indeed, members of the Organisation of the Petroleum Exporting Countries are more dependent on oil now than when prices fell sharply in 1985-86 and 1997-98. Exports plummeted in value after the Opec basket price fell from $27 a barrel to $13.50, and from $18.70 to $12.30, respectively. But in 1985 and 1997, oil exports were just 21 per cent of Opec’s gross domestic product, compared with 36 per cent now.