Crude oil prices have plunged by $25, or more than 20 per cent, since mid-June, raising many questions. How low might prices go? If they rebound, at what level will they stabilise? Will Saudi Arabia and Opec move to cut output when they meet next month? At what price level might US shale oil production be affected and how severely?

One thing is certain: even the current lower prices are rapidly creating winners and losers. Losers are producers, countries and governments. If Brent falls to $80, Opec countries would lose some $200bn of their recent $1tn in earnings, affecting not only their ability to earn enough to cover the post-Arab Spring expanded budgets, but also their capacity to service debt without triggering defaults. And for the US, if prices fall much further, capital expenditures to expand production would have to be cut, potentially slowing the US shale revolution.

On the other hand, the world economy as a whole would enjoy the equivalent of a huge quantitative easing programme, helping to spur sputtering economic growth. The decline in prices would generate a $1.8bn daily windfall, some $660bn annualised. Tracking this into gasoline prices, in the US, where last year some $2,900 per household was spent on gasoline, the windfall would amount to a tax rebate of just under $600 per household. It would affect all consumers globally save for those in Opec countries, who already pay little for fuel.