Pakistan's oil mafia is alleged to have siphoned Rs.90 billion annually during former president Pervez Musharraf's tenure by supplying substandard diesel at the rates of the high quality premium variety, a media report said Saturday.

Some key officials of Musharraf's presidency, the petroleum ministry, the Central Board of Revenue, marketing agency Pakistan State Oil (PSO) 'and even some top rulers of that time are believed to have multiplied their fortunes', The News said.

The previous government disallowed probe into 'what could possibly be the biggest scandal of the military rule' while the present government was also sitting tight on the issue, the newspaper said.

The National Accountability Bureau (NAB), during Musharraf's regime, had initiated an inquiry into this scam 'but was immediately given a shut-up call by the dictator', the newspaper said, adding that in its preliminary finding, NAB estimated misappropriation of Rs.90 billion annually on account of the import of substandard diesel.

The then-NAB chairman, Lt-Gen (retd) Shahid Aziz, when contacted, confirmed the estimated annual figure of Rs.90 billion and said it was possibly one of the biggest corruption scandals of the Musharraf regime but still remained untouched.

'This particular inquiry that we had initiated was different from the one on oil price mechanism,' the retired general said, adding that through random raids, NAB had collected samples of diesel from oil tankers and petrol pumps and found them below the declared specifications.

According to a source, NAB, in its preliminary inquiry, established that substandard diesel was imported at lower rates but was supplied at higher rates as a premium product with less than 0.5 percent sulphur content.

'The oil mafia has earned so much money that if each major beneficiary of this loot and plunder starts spending Rs.10 million a day, he would even then be never short of money in his whole life,' the source said, adding that Musharraf was well aware of the scam but looked the other way.

Musharraf was in office 1999-2008 but the period during which the scam occurred was not immediately clear.