The share of the world's oil reserves controlled by the big Western oil companies, such as BP, Shell and ExxonMobil, has fallen to less than 10 per cent, compared with 70 per cent in 1978.

The world's reserves are dominated increasingly by government-controlled national oil companies in big producer countries such as Saudi Arabia, Russia, Iran and Venezuela. These groups control about 90 per cent, according to a book due to be published this year. The figures in the book point to the diminishing power of international oil companies by comparing the reserves held by what were in 1978 the eight largest global oil companies — Exxon, Shell, BP, Gulf, Texaco, Mobil, Socal (Chevron) and the Compagnie Françaises Des Petroles (CFP-Total) — with those of the five companies they have merged into today.

“In 1978, these companies together held roughly 70 per cent of world reserves,” Wajid Rasheed, the author of The Hydrocarbon Highway, says. “Today, there are ‘five sisters': ExxonMobil, Shell, BP, ChevronTexaco and Total and their reserves amount to approximately 10 per cent of world reserves.”

Reserves in countries such as the United States and Britain have been sharply depleted while “resource nationalism” has led national governments in other producer regions to nationalise their oil assets, to adopt new sharing agreements or to eject Western companies altogether.

ExxonMobil, the largest of the “five sisters'', has estimated reserves of 11.8billion barrels of oil. BP, which is to report annual results tomorrow, holds 9.8billion. Such figures pale in comparison with some of the big national oil companies: Saudi Aramco, the state-controlled producer in Saudi Arabia, claims to have 264billion barrels, about a quarter of global reserves.

Furthermore, much of the world's oil controlled by these national companies is the easiest and cheapest to produce, Mr Rasheed argues. Saudi oil, on average, costs only about $2 per barrel to produce onshore, compared with $26-plus per barrel for oil produced from Canada's bitumen-rich oil sands.

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