Abdallah Jumah, president and CEO of the state-owned Saudi Arabian Oil Company, better known as Aramco, said the world has potentially 4.5 trillion barrels in reserves - enough to last 140 years at current levels of consumption.

"The world has only consumed about 18 per cent of its conventional potential," Jumah said, rejecting fears that supplies will run out in a few decades.

Experts have estimated that the Earth's recoverable oil resource is between three trillion and more than four trillion barrels. If consumption rises about two per cent a year from today's levels of about 85 million barrels a day, the low end of that range would only be enough to last until 2070.

Rex Tillerson, the chairman of Exxon Mobil, has said that world demand for oil will increase by 50 per cent in the next decade.

Jumah said new technology and better recovery rates would make it possible to find enough new oil resources to add one trillion barrels to world reserves over the next 25 years.

Gulf of Mexico find

Drilling is now going on as deep as 3,000 metres below the Gulf of Mexico and between 2,100 and 2,500 metres elsewhere. Experts say a newly discovered petroleum pool beneath the Gulf of Mexico eventually could yield anywhere from three billion to 15 billion barrels.

Industry leaders have gathered in Austria this week for a conference sponsored by the Organisation of Petroleum Exporting Countries.

Earlier this week, the 11-nation group agreed to maintain its current production target of 28 million barrels a day but made clear it would consider a cutting its output before the end of the year if oil prices continue to fall.

Crude prices have fallen to a five-month low, dropping by more than $12 a barrel since record highs in mid-July. Analysts say ample supplies and the easing of political tensions in Lebanon and Iran have driven prices lower.