The importance of ensuring world's oil artery flows freely

The Strait of Hormuz is one of the arteries of the global economy. Twenty per cent of the world's oil passes through these waters. Now fresh worries are cast on its safety as the UAE coastguard says a mysterious explosion just after midnight on the Japanese tanker M Star on July 28 was a terrorist attack. The blast caused little damage and the M Star was able to continue its journey on Friday. Claims of responsibility from the little-known Abdullah Azzam Brigades were met with scepticism by experts.

Of the world's maritime "choke points" through which oil supplies must move, such as the Suez Canal and Bosphorus Straits, Hormuz is by far the most important. It carries the largest quantities of oil - about 17 million barrels a day - as well as all the liquefied natural gas sent from Qatar, the world's leading exporter. Alternative pipelines run to Yanbu on Saudi Arabia's Red Sea coast and there is an often-sabotaged route from Iraq to Turkey. The line from Habshan in Abu Dhabi to Fujairah will also help to bypass Hormuz when completed. Still, all these pipelines can handle only a fraction of Gulf production.

The most obvious threat is a more successful repeat of the M Star incident, if indeed it was a terrorist attack. In 2002, the French tanker Limburg was rammed by an explosives-laden boat off Yemen, killing one crew member and causing 90,000 barrels of oil to leak into the Gulf of Aden. But the Limburg did not sink and was towed to Dubai for repairs. Such attacks seem unlikely to happen often in the Gulf. The shipping lanes pass the coast of the UAE and Oman, not the lawless shores of Yemen and Somalia with their pirate havens.

The UAE and Omani navies, recently augmented, patrol the waters with US support. No doubt security will be further beefed up after the Japanese tanker explosion. Strategic planners are more worried by the prospect, one day, of a military confrontation in the Gulf. The strait is 54km wide and between 25 metres and 40 metres deep so, unlike the Suez Canal, it could not be physically blocked. Menaces to shipping might include anti-ship missiles, sea mines or "swarming" attacks by small boats. There are numerous small islands and indented coastlines around the strait that could serve as bases for terrorists or weaponry.

No doubt, as in the Iran-Iraq war, a number of vessels could be struck. They might burn or sink, although tankers are surprisingly resilient. Insurance premiums would rocket, shipowners would be reluctant to risk their vessels except for high freight rates and there would be panic over oil supplies. At the worst point of the Iran-Iraq conflict, shipping in the Gulf was reduced by a quarter. Yet there are good reasons why it would be very hard to block the strait completely. For technical reasons, targeting ships around Hormuz with radar is difficult and vulnerable to counter-measures.

Laying a complete carpet of mines would take at least a week. Mine-laying would probably be detected and minesweepers already based in the Gulf could clear a shipping channel within a few days. Any attempt to block the strait would be an attack on the vital interests not only of the US but also of the Gulf countries, plus Europe, China, India, Turkey and Japan. If any one of these tried to shut off Hormuz, all of the others would welcome military intervention to restore access.

Among the world's leading states only Russia could possibly benefit from the rise in oil prices that would accompany such a conflict. Since the 1970s oil crises, members of the International Energy Agency, essentially the developed countries, have committed to holding 90 days of oil imports in reserve, a margin that could be extended by conservation measures. China is also increasing its strategic oil holdings. Due to weak demand, US commercial stocks of oil are at a 20-year high, although that could change.

With Hormuz unlikely to be entirely closed for more than a month, this gives the oil importers staying power, enabling them to survive a temporary disruption. For these reasons, a serious attempt to close Hormuz only seems likely in an extreme situation. Much more likely and effective would be some kind of asymmetric warfare directed against softer targets in the region. Perhaps attacks might be staged on vulnerable infrastructure such as ships in port (as with the USS Cole, bombed in Aden in 2000), Iraq's Basra Oil Terminal or Qatar's offshore gas platforms.

The continuing violence in Iraq shows how exposed pipelines in particular are as they snake through remote terrain. But despite all of the sabotage Iraqi production, though not increasing, has not been shut down either. Hormuz is a vital waterway for the world and for the UAE. It merits careful surveillance and planning for contingencies, however unlikely. The strange incident of the M Star is a reminder of that but no more.

Robin M Mills is a Dubai-based energy economist, and the author of The Myth of the Oil Crisis