“Big” and “oil” are mentioned so often in the same breath that it is easy to lose perspective. Motorists and environmentalists never tire of berating the dominant supermajors whose petrol stations and share listings make them the public face of the industry, their favourite target being America's ExxonMobil. If market value was the sole magnet for opprobrium, then Exxon's executives could breathe a little easier as PetroChina recently overtook it as the world's most valuable listed energy company.

But there is “big oil” – last year, Royal Dutch Shell, for example, earned more than $1bn a month – and then there is bigger oil. No oil major is able to affect energy prices on its own and even Exxon is far smaller than the world's largest energy company. It is not even close. Saudi Aramco's estimated hydrocarbon reserves of 300,000m barrels of oil equivalent make it 15 times Exxon's size. Exxon comes in about 17th place, with the top 10 being entirely state-owned.

PFC Energy, which recently ranked the top 50 publicly listed energy companies in the world, notes that their combined market value was $3,900bn at the year-end. Impressive? Not really, particularly since much of this float is not in private hands, including as it does several companies such as Rosneft, Gazprom, Petrobras and PetroChina itself with state shareholdings.