When Fadel Gheit first warned of his "nightmare scenario" that Saudi Arabia's main oil export terminal at Ras Tanura could be wiped out by terrorists, he was dismissed as an alarmist.
It was the week after the September 11 attacks in New York, where he is based. But the oil analyst began to think there was another target that would have an even more devastating impact if hit.
As fears of upheaval in Saudi helped set world crude oil prices to 21-year highs of $42.45 per barrel ahead of an Opec ministerial meeting today, there were fewer willing to scoff at Mr Gheit.
"I cannot think of any more logical target for terrorists. It [Ras Tanura] is the nerve centre for the Saudi oil trade but also for global exports. If you can blow up the Pentagon in broad daylight, then it cannot be impossible to fly a plane into Ras Tanura - and then you are talking $100 [per barrel] oil," he says.
Saudi Arabia is the linchpin for world crude supplies, a key to setting prices and yet sitting on a political tinderbox due to internal dissent and having trouble securing itself against terrorism.
The repressive desert kingdom is the birthplace of Osama bin Laden, provided 15 out of the 19 attackers on 9/11 and its future problems could ultimately make petrol too expensive for us to take our cars out of the garage.
Not only is Ras Tanura or the refining centre of Abqaiq dangerously exposed to being knocked out of action by militants, but Mr Gheit also believes regime change in Saudi to a more hostile Islamic government is as inevitable as it was in Iran a quarter of a century ago. "It's only a matter of time," he claims.
But this is no headline-grabbing polemicist. The Egyptian-born American is employed by investment house Oppenheimer & Co to provide sober assessments of future oil supply and demand to investors sitting on billions of dollars worth of Wall Street financial funds.
Nor is he an armchair theorist. The 58-year-old worked in Saudi as a chemical engineer for Mobil (now ExxonMobil) while it was building facilities at Yanbu in the 1980s. Yanbu, on the Red Sea, was attacked barely a month ago and six western expatriate oil workers were killed; in a further attack in Khobar at the weekend 22 civilians were killed. Yesterday shots were fired at US military personnel outside the capital Riyadh, adding to the tension and forcing a Saudi foreign affairs spokesman, Adel Al-Jubeir, to admit the oil industry was being targeted.
An assault on Ras Tanura, however, would be vastly more serious. As much as 80% of the near 9m barrels of oil a day pumped out by Saudi is believed to end up being piped from fields such as Ghawar to Ras Tanura in the Gulf to be loaded on to supertankers bound for the west.
Ras Tanura and other terminals are heavily patrolled and protected, the energy ministry is ringed by concrete and the streets outside patrolled by tanks and armoured vehicles. But that seems to have done little to reduce a growing number of attacks on key installations. Saudi is vital because it sits on the world's largest oil reserves, exports much more than anyone else and even more importantly has consistently acted as "swing producer" inside the Organisation of Petroleum Exporting Countries (Opec) to try to iron out supply/demand blips.
The Saudi royal family promised ahead of the western assault on Saddam Hussein that it would pump out more crude to make up any temporary shortfall should Iraqi oilfields be knocked out of action. Similarly, Saudi promised to increase its output unilaterally when its plan for Opec to increase production was turned down by some other Opec ministers ahead of the meeting in Beirut today.
But this role of being friends to the west causes tension inside the country with religious and other conservatives opposed to social liberalism and western culture.
Against this is a growing number of young, highly educated Saudis who want to throw off what they see as the semi-feudal rule by the House of Saud and adopt democracy and a new openness.
So what would happen if either Ras Tanura was put out of action or the country was taken over by an anti-western fundamentalist movement which decided to turn off oil to the west?
Julian Lee, senior energy analyst at the Centre for Global Energy Studies thinktank in London, does not dismiss out of hand the $100 per barrel oil scenario which could produce the £10 gallon of petrol. "I think it would be difficult to put an upper limit on the kind of panic reaction you would see in the global oil markets following the loss of Saudi supplies," he says.
And $80 plus could be a more likely guess, according to Mr Lee. But he also believes it would be a relatively short-lived spike because the west would take reserves out of storage to try to stabilise the market.
The US has close to 700m barrels of oil in its strategic petroleum reserves while many European countries, plus Japan and South Korea, have similar stocks. Britain is still a net exporter, so in theory is self-sufficient but even if the direct impact of a loss of Saudi oil was not felt directly for say half a year, the shock would produce serious disruption and probable economic recession.
And if an extreme Saudi regime produced oil but refused to sell it to the west? Mr Lee suggests an invasion by America could not be ruled out but seems pretty unlikely given the difficulties in Iraq.
Saudi exports would be sucked up by China, Asia and others but in turn a lack of demand for non-Saudi supplies from those nations could then be passed on to the west, he argues. But that is not to say there would not be a problem even if Russia, Angola and the Caspian nations are all busy providing new sources of crude.
"There is no one who could step in and take over from Saud after six months, one year or even two," says the analyst from the Centre for Global Energy Studies. "But the world has lived with being dependent on politically shaky countries: look at the coup after coup in Nigeria, strike after strike in Venezuela," he argues.
Not everyone is willing to even consider the "nightmare scenario." Gerald Butt, an editor with the Middle East Economic Survey (MEES) newsletter, is dismissive of suggestions that the country is in a politically fragile state. "The royal family is very large and very influential. It will stand together to face a common threat and sees al-Qaida as a security issue and not a political one," he says.
As for the threat to oil installations, the MEES editor believes they are well guarded, pushing terrorists to attack softer targets such as compounds of western workers.
In Beirut, the Saudi oil minister, Ali al-Naimi, assured the meeting of Opec last night that oil facilities in the kingdom were "very secure". He said: "The paranoia about terrorism in the world threatening all the oil establishments in the world, that's not true."
Back over the Atlantic, Mr Gheit remains convinced that there is a real and continuing threat which would cripple the world economy. He was in the past accused of being irresponsible by critics who said doom mongers had been predicting regime change in Saudi for 20 years, but the current situation frightens economists and consumers alike. However there is one group that is happier than others.
Oil giants such as BP in Britain and ExxonMobil in the US have been making corporate history by notching up the largest profits ever.
As Mr Gheit puts it: "Oil executives must be pinching themselves every morning when they wake up. They are not making money, they are printing it."