We use more oil than we find, and if producers are fixing their figures the end could be closer than thought

Predicting the end of the age of oil can be a sticky business. The Association for the Study of Peak Oil and Gas (Aspo), a collection of industry figures, politicians and academics, this week held its annual meeting at the Gulbenkian Museum in Lisbon.

From quiet beginnings three years ago, Aspo is no longer just "bubbling under" in being taken seriously. Delegates had to squeeze past no fewer than 10 documentary crews, a nest of television cameras and a phalanx of reporters just to grab their seat in the packed auditorium.

Rather than talking about when oil could "run out", Aspo prefers to predict that global production may be at, or approaching, its height. The world is using more oil than it finds, and discoveries of oil fields peaked in the 1960s. Despite technological advances since then, new field discoveries are at an all-time low. This, said delegates, has led to the current lack of any "cushion" between supply and demand, and to the consequent high prices. The outcome for the world, if Aspo is correct, is catastrophic.

Central to the organisation is the work of Colin Campbell, a geologist and former executive vice-president of oil giant Total. Making the meeting's keynote speech, Campbell talked about the "dawn of the end of the age of oil" and the "end of economics".

Underpinning all of Campbell's, and Aspo's, work is the lack of transparency in the world's oil data. Campbell drew attention to the way in which members of the Organisation of Petroleum Exporting Countries (Opec) "revised" their reserve figures in the 1980s, and said that it is incredible that this "flawed data" is still being used today. He highlighted the example of Kuwait, which scrubbed its previous figures in 1985. Overnight, its reserves went from 64bn barrels to 92bn barrels. As Opec allows production quotas tied to stated reserves, this allowed Kuwait to pump more oil and immediately make a lot more money.

Campbell showed how, two years later, the other countries in Opec, outflanked by Kuwait's sudden action, followed suit. The United Arab Emirates went from 31bn barrels to 92bn barrels. "Then came Iran," said Campbell. It declared its reserves had increased, but went one better, going from 47bn barrels to 93bn. "And what of Iraq?" added Campbell. "Saddam, as we all know, had some pretty strong views on things, so he decided to come in at a round 100." Its previously stated reserves were 47bn barrels.

Some 18 to 20 years later, these numbers remain unchanged. This despite the United Arab Emirates, for instance, pumping millions of barrels every week since the day it flipped its figures.

Campbell asserts that Opec members, and others such as Russia, are stating the total amount ever found, not the amount left for us to use. But such claims are not the preserve only of Aspo. This year, the International Energy Agency, the International Monetary Fund and G7 members all demanded that Opec, and other producer nations, open their fields to audit. Without knowing how much oil is left to pump, decisions about any energy transitions - the move away from oil as a predominant fuel - remain impossible.

Saudi Arabia, a major player in global oil production, in 1988 also increased its stated reserves - from 170bn barrels to 258bn barrels overnight.

Just days before the Aspo meeting, Ali al-Naimi, Saudi Arabia's oil minister, claimed the desert kingdom could move from producing around 9m barrels a day, to 12m or even 15m. This has been consistently stated but, so far, unfulfilled by the kingdom and its state oil company Saudi Aramco. What is more worrying is that Naimi for the first time put a limit on that level of production: around 15 years. Previously, the Saudis had said they could pump at this level for 50 or even 100 years.

Matthew Simmons, Aspo delegate, adviser on George Bush's energy plan, and investment banker, is a leading expert on Saudi oil production. He is sceptical about all the Saudi figures and his book on the subject, Twilight in the Desert, is causing waves in the industry, despite not hitting the shelves for another fortnight.

"No one can know how much oil Saudi Arabia has left underground," Simmons says. "A handful of people at Saudi Aramco think they know, but no one really does. Why? Because Saudi Aramco has a kind of omerta, a code of silence that runs through it.

"I met a guy a few years back, at a conference where I was the keynote speaker. He was a senior engineer working for Aramco, senior enough to be flown to Houston to hear me speak. Afterwards, I asked him the size of Saudi Arabia's biggest field, Gharwar. Not in terms of reserves, just its physical size. It was something I could have looked up on a map, but I thought I would just ask him. He said: 'It's about 130 miles long and 15 to 20 miles across, but don't ever tell anyone at Aramco I said that or I'll lose my job.'"

This revelation set Simmons thinking. "How could this senior figure be so scared?" he asks. "After all, he wasn't telling me anything I couldn't have found out myself. It amazed me and set me looking at Saudi production in a whole new light."

Now Simmons believes that Gharwar, the biggest oilfield on the planet, is definitely in decline. "It's got to be," he says. If he is right, there is little left to replace it and the beginning of the end of oil could be upon us sooner than we think.