According to the London-based newsletter, NIOC overtook Petroleos de Venezuela in its rankings based on six operational criteria covering 2003 - oil and gas reserves, oil and gas output, refining capacity and product sales.

Earlier this month, the new online business publication Dinar Standard rated NIOC as the second largest company in the Muslim world based upon revenue.

PIW does not include total revenues in its rankings due to the wide difference in accounting practices but lists NIOC's income as Dlrs 28.4 billion, Dlrs 10 bn less that the total revenue estimated by Dinar Standard, which was extracted from OPEC data for 2003.

Middle East and North African national oil companies continue to dominate the world list, which is headed by Saudi Aramco, whose revenue, although not a criteria, was Dlrs 10 bn more that the Dlrs 83.1 bn calculated by Dinar Standard.

Other regional companies include Kuwait Petroleum and Algeria's Sontrach, listed as equal 12th and Abu Shabi National Oil Company at 14th.

Iraq National Oil Company moves down one place to 22nd, but remains just ahead of Libya's National Oil Corporation. The Egyptian General Petroleum Corporation and Qatar Petroleum are ranked as 25th and 26th respectively.

ExxonMobil of the US remains the top oil company in the west and second in the world, while Anglo-American BP moves up to joint second place and joint fifth in the world with Royal Dutch/Shell Group.

In terms of annual revenue, western firms remain way out in front, led by BP as the richest with Dlrs 236 bn, ahead of ExxonMobil's Dlrs 223 bn and Royal Dutch/Shell Group's Dlrs 205 bn.