Is the world running out of oil? A debate that has been going on worldwide for some 50 years, and in the United States for more than 80 years, has been publicly stirred up again by a recent newspaper interview with the chief economist at the International Energy Agency in Paris.

Talking to The Independent in London, Fatih Birol says that world crude oil production is set to peak in about 10 years. But an "energy crunch" could start as soon as next year, he warns, with soaring oil prices threatening to derail any recovery from the current world recession.

Most economists believe the recession-induced slowdown in oil demand in 2009 has helped give the world more breathing space. Even the IEA's own Medium Term Oil Market Review up to 2014 sees more than adequate world oil production potential to meet projected demand, with OPEC -- above all Saudi Arabia -- continuing to maintain a reassuring cushion of spare capacity.

Birol's comments have given semiofficial backing to some of the shriller warnings of so-called peak oilers. They argue that governments must act immediately to wean the world economies off the energy source that fueled the 20th century's massive economic growth and remains an essential component of modern lifestyles.

Initially regarded as mavericks and cranks, peak oilers are a disparate group of economists and geologists -- some with senior experience in the international oil industry -- who believe world oil production is about to go into irreversible decline. History is not on their side.

They challenge the consensus view of the international oil industry that proven world oil reserves are likely to go on increasing -- as they have for most of the last 100 years. Even though fields in some parts of the world may have passed their production peaks, industry spokesmen are generally confident that reserves are adequate to sustain or even, if needed, to increase current production levels.

They cite a number of factors: the political opening up of areas that are under-explored, more sophisticated exploration techniques, advances in secondary and tertiary recovery that allow a greater proportion of oil in place to be extracted, unconventional sources of oil like the huge Canadian and Venezuelan tar sands, and, critically, the expected boost to exploration and research resulting from the prospects of higher prices.

Indisputably, oil in the Earth's crust is a finite resource. But the same is true of stone, say some energy economists. "And the Stone Age didn't end because the world ran out of supplies of stone." Stone was replaced by other, better materials more suited to early man's slow technological advance.

The same, they believe, is likely to happen with oil, prompted and accelerated by the price signals sent out by global energy markets. Birol's comment: "One day we will run out of oil, it is not today or tomorrow, but one day we will run out of oil and we have to leave oil before oil leaves us, and we have to prepare ourselves for that day."

Oil historians point out that major oil company geologists have always publicly underestimated the size of current and future reserves. Pessimistic reserve estimates have helped the industry over time to lobby for lower taxes.

Proven oil reserves at the end of 2008, according to BP's 2009 Statistical Review of World Energy, were virtually unchanged from the year before but some 25 percent higher than 10 years earlier. Over the decades, new discoveries and reserves upgrades have more than matched global oil consumption.

The comforting view taken from history is under geological challenge. Underlying Birol's pessimism, the IEA reports that an unprecedented field-by-field analysis of the historical production trends of 800 oil fields indicate that decline rates are likely to rise significantly in the long term.

Peak oilers say they have been singing that tune for many years.

The study is in line with conclusions reached in 2004 by oil investment analyst Matthew Simmons that Saudi Arabia's ability to sustain, let alone increase, its production capacity was severely limited by the decline reserves of its largest fields.

Simmons' work, based on detailed examination of early technical papers by Aramco geologists, was hotly contested by Saudi officials. But Saudi Arabia, like most OPEC members, still steadfastly refuses to divulge any detailed oil reserve or production data, but claims to be adding some 2.5 million barrels a day of capacity.

How long it can sustain that capacity may hold the key to when the world runs out of spare oil capacity -- at any price.