His proudest moment was a major find in Algeria. My friend studied the data and walked the ground, but the scientific findings were ambiguous, a common development as oil geologists will tell you. In the end, he had a hunch that there was a decent reservoir, recommended drilling and struck oil. Was he a genius or was he just lucky? Probably a bit of both.

Ali Naimi, the former shepherd who rose to become the first Saudi chief executive of Saudi Aramco and then Minister of Petroleum & Mineral Resources, is not a superstitious man. Like my friend, he is a geologist. Nobody can seriously claim to have more knowledge of Saudi Arabia's oil and gas reservoirs. And yet, he has a gut instinct about the possibilities under his feet. 'Geologists are optimistic,' he said recently. 'I believe there is a lot of gas in the Rub al-Khali [Empty Quarter].'

The intuitive approach to the industry is displayed by Matthew Simmons, the investment banker and energy analyst, who caused a huge stir last month with his claim that Saudi Arabia's oil production could soon go into steep decline because of the degrading condition of the kingdom's biggest oil fields, notably Ghawar. Railing at the conventional wisdom that Saudi Arabia can with sufficient investment lift output to meet rising demand and fill supply gaps, Simmons in a book and several presentations said he got a bad feeling about the kingdom's oil reserves after reading 200 papers published by the Society of Petroleum Engineers (SPE) and a recent visit. 'I am not a petroleum geologist or reservoir engineer,' he proudly told a conference in Washington on 24 February. 'The dots did not seem to connect.' So Simmons, the non-geologist, has hunches - pessimistic ones.

Simmons' most substantial piece of 'evidence' is the decline in oil output in neighbouring Oman, where the forecast is for crude production to fall to 630,000 barrels a day (b/d) this year. As delegates at MEED's Major New Project & Investment Opportunities conference in Muscat heard on 24 February, the world's biggest and most ambitious enhanced oil recovery (EOR) programme has been launched in the sultanate. Simmons suggests that it is likely that similar problems are being displayed by the kingdom's even older onshore fields.

Roused by the extraordinary charges, and the enthusiastic reception they received in the US media, Saudi Aramco sent two of its top geologists to the same Washington conference to publicise the kingdom's rebuttal. If anything, recoverable Saudi oil reserves are underestimated, they declared. Ghawar is not in trouble and the Shaybah field, in production since 1998, could pump at its present levels for a half-century. The kingdom can comfortably maintain 10 million b/d of oil production for half a century and could if required get output to 15 million b/d. More geologists. More optimism.

The presentation went some way to dealing with the Simmons thesis, but fell short of a complete repudiation. Nevertheless, even sceptics were obliged to concede that the Simmons case looks a lot weaker.

So what can an outsider conclude? It seems that the oil industry is driven by faith as well as logic. If you do not like Saudi Arabia, or have invested in Russia rather than the Gulf, the report of declining output from the kingdom confirms an established prejudice. But if you have the opposite view, the Simmons thesis is a politically-charged exaggeration lapped up by Saudi Arabia's enemies.

The clash of perspectives will manifest itself this month when the kingdom signs contracts for new gas exploration licences with Eni and Repsol, Lukoil and China Petroleum & Chemical Corporation (Sinopec). Missing from the list of partners will be BP, ExxonMobil and ChevronTexaco. Their geologists have used science to prove there is not enough gas to be found to justify the investment.

But the newcomers to Saudi Arabia may have a more artful way of finding it. A hunch.