TANKERS are legitimate targets for Islamist terrorists, according to a pronouncement from a prominent Saudi al-Qaeda ideologist.
Pipelines and other infrastructure controlled by 'infidels' are also singled out for inclusion in the guidelines.
However, oil wells should be spared as they represent an economic lifeline for Muslim nations, supporters are advised.
Coming hard on the heels of last week's frustrated attack against the world's largest oil processing plant at Abqaiq, the news will concern many in both the shipping and oil sectors.
Islamist terrorists have turned on tankers before, most notably blowing up French-owned VLCC Limburg in Yemen in October 2002.
However, security specialists yesterday said that security precautions in many Saudi ports have been substantially beefed up. They also contended that the strategy might not be universally backed in the terrorist camp.
The instructions come in a manifesto written by Abdulaziz al Enezi, an al-Qaeda militant captured by the Saudi authorities last year. The two-year-old document was recently posted on an Islamist website.
Mr Enezi argues that disrupting oil supplies is the best way to damage the US economy and to destabilise the Saudi regime.
Saudi state-owned refineries and oil pipelines, as well as Iraqi facilities, are described as 'all in the hands of infidels'.
In edition, Mr Enezi writes: 'It is permissible to target oil interests held by infidels ... including American and Western oil tankers.'
He added that oil pipelines are easy targets because their length makes them difficult to protect.
Moreover, attacks on them do not directly detract from Muslim oil wealth.
Experts say that Mr Enezi had the rank of 'information minister' in al-Qaeda's Saudi offshoot, and acted as a spiritual guide to the group.
But analysts close to the Lloyd's market yesterday pointed to countervailing tendencies.
Zaineb al Assam, head of the Middle East division at strategic intelligence forecasters Exclusive Analysis, said that while oil infrastructure was a target for terrorists, the risk was mitigated by the resistance of some local cells to leadership calls to action.
'This is precisely because they seek to inherit the kingdom's oil wealth rather than to destroy the infrastructure that helps generate it.'
But Ms al Assam added there was a lack of uniformity surrounding strategy to weaken the House of Saud, and therefore the target-set was not necessarily fixed.
'Attacks on expatriate workers in the oil industry are far more likely than on the facilities themselves because they accomplish both objectives of weakening the regime and diminishing the western footprint in the kingdom,' she said, adding that security measures such as anti-aircraft batteries which provide cover for ports involved in the export of hydrocarbons had been put in place to counter the threat.
'With respect to offshore protection and the safeguards given to tankers carrying Saudi crude, both air and sea forces and Aramco are deployed to protect critical resources,' she said.