When the price of crude oil goes through one of its periodic downturns, as it is doing now, it sends a shiver through the oil industry. History promises that higher prices will return. Until then, US shale companies are under severe pressure and big oil companies wonder about the viability of new projects.

There is more to worry them this time: not just the 29 per cent fall in the price of Brent crude since the start of October as Russia and Saudi Arabia pump more oil, but the fear of this bear market enduring. The romance of oil exploration is fading at companies such as Royal Dutch Shell, BP and ExxonMobil as they rethink the way they have operated for decades.