Little more than a year ago PetroChina, the oil company largely owned by the Chinese government, surpassed ExxonMobil to become the world’s biggest listed energy group. It was the first time in oil’s history that a national oil company had boasted the industry’s largest market capitalisation.

Months later, Alexei Miller, chief executive of Gazprom, confidently asserted that within a decade the Kremlin-controlled gas monopoly he headed would be the world’s largest energy company with a market capitalisation of more than $1,000bn.