A failed al Qaeda attack on a Saudi oil facility last week may have seemed poorly planned, but determined militants, boosted by experience in Iraq, will keep the key oil sector in their sights, analysts said.

Security police killed suicide bombers riding what appeared to be cars of the Saudi state-owned oil company Aramco as they tried to drive into the heart of the world’s biggest oil processing plant at Abqaiq on Friday.

An al Qaeda statement later said the radical Islamist network headed by Saudi-born Osama bin Laden was behind the attempt to penetrate the desert site in the Eastern Province, where most of Saudi Arabia’s oil wealth lies.

Analysts say massive security is deployed around the region’s oil sites, and the fear that such attacks may one day hit their target is one of the Saudi royals’ worst nightmares.

This was the first direct attack on a major oil target in three years of al Qaeda violence against the US-allied royals.

The campaign had largely run out of steam over the past year — Friday’s attack was the first major operation since suicide bombers tried to storm the Interior Ministry in Riyadh in December 2004 — and the government had hoped it had largely seen the back of it. “Societies are not transformed overnight, and effective and lasting change takes time. But we have started, and I believe turned the corner,” Foreign Minister Prince Saud al-Faisal said last month.

“And we shall persist, God willing, and prevail. This is a struggle that we are determined to win, and cannot afford to lose.”

Kevin Rosser of British-based Control Risks Group said the oil industry had always been a target. “Everybody knew it,” he said.

But he added: “The Saudis need to ensure they have a high level of vigilance because there is no room for complacency. It’s unrealistic to expect that the terrorist problem will disappear overnight or be waved away with a magic wand.”

A successful strike on the Saudi oil industry would be a major coup for al Qaeda, hitting at the heart of a decades-old alliance between the Saudi royals and Washington which Arab opposition groups across the region dream of seeing in ruins.

Oil prices jumped $2 a barrel on news of the attack in the world’s largest oil exporter, which came a year after bin Laden urged his supporters to hit Gulf oil targets. The government said oil and gas output had been unaffected.

“They did this in a hurry. If it had been done in a better way it could have had an enormous effect,” said Mohammed al-Mas’ari, a London-based dissident who Saudi Arabia has accused in the past of having links to al Qaeda. The majority (of militants) are tied down in Iraq right now. When it settles down, some will come home to carry the struggle further. They will be better trained with more tactical skill. Then the regime will have greater difficulties.”

Saudi security analysts estimate that 2,500 Saudis were in Iraq during 2003-4, fighting as part of the Sunni-led insurgency against US forces and the Shi’ite Muslim majority that came to power together with ethnic Kurds after the 2003 war.

“This attack doesn’t actually differ in essence from any other attack over the last three years. It’s just a question of how well-protected the installations are or not,” said Mansour Alnogaidan, an analyst and former Saudi militant.

“The Islamist extremists look at this plant as the secret of the Al Saud family’s survival and they think they can destroy them by attacking the oil sector.”

Some Saudi reformers said the attack would further isolate bin Laden’s supporters in Saudi Arabia, where they are thought to have lost much public sympathy after Muslims and Arabs were killed in attacks on foreign residential compounds.

“Those who target economic installations are targeting the domestic economy, the bread that people eat every day,” moderate Islamist Mohsen al-Awajy said. “It has nothing to do with occupiers and the Americans.”

But Alnogaidan and Mas’ari said there was not enough evidence to be sure that the militants are an isolated minority. “Saudi Arabia is a society where everything is in the dark. It’s like black hole, where it’s difficult to know people’s point of view. There are no opinion polls,” Mas’ari said. He said that Saudi Islamist websites where users now often condemn al Qaeda had been infiltrated by security apparatus.

Alnogaidan added: “Al Qaeda has been struck badly but it is too soon to say it is defeated in Saudi Arabia.”