There is more than twice as much oil in the ground as major producers say, according to a former industry adviser who claims there is widespread misunderstanding of the way proven reserves are calculated.

Although it is widely assumed that the world has reached a point where oil production has peaked and proven reserves have sunk to roughly half of original amounts, this idea is based on flawed thinking, said Richard Pike, a former oil industry man who is now chief executive of the Royal Society of Chemistry.

Current estimates suggest there are 1,200 billion barrels of proven global reserves, but the industry's internal figures suggest this amounts to less than half of what actually exists.

The misconception has helped boost oil prices to an all-time high, sending jitters through the market and prompting calls for oil-producing nations to increase supply to push down costs.

Flying into Japan for a summit two days after prices reached a record $139 a barrel, energy ministers from the G8 countries yesterday discussed an action plan to ease the crisis.

Dr Richard Pike explains his claims

Explaining why the published estimates of proven global reserves are less than half the true amount, Dr Pike said there was anecdotal evidence that big oil producers were glad to go along with under-reporting of proven reserves to help maintain oil's high price. "Part of the oil industry is perfectly familiar with the way oil reserves are underestimated, but the decision makers in both the companies and the countries are not exposed to the reasons why proven oil reserves are bigger than they are said to be," he said.

Dr Pike's assessment does not include unexplored oilfields, those yet to be discovered or those deemed too uneconomic to exploit.