"After this third party review by our external auditors, the Tawke oil field is confirmed to be a world class, giant oil field," DNO chief Helge Eide said in a statement.

The audit, carried out by French company Beicip Franlab, showed the field, which currently produces an average of 70,000 barrels of oil a day, had recoverable reserves of around 636 million barrels, up from an estimate at the end of 2010 of 306 million barrels.

"The new reserves numbers far exceed our expectations of even a few months ago and certainly were not envisaged when we made the discovery in 2006," Eide said.

Following the announcement, DNO saw its share price jump 3.83 percent to 6.24 kroner in midday trading on an Oslo stock exchange down 1.8 percent.

DNO, which was among the first companies to operate in Iraq after the fall of Saddam Hussein, meanwhile said it had separately "undertaken to estimate the size of other discoveries on its licenses in the Kurdistan region of Iraq as well as the potential of all undrilled prospects and geological horizons in response to a request by the Kurdistan Ministry of Natural Resources."

Those non-audited estimates showed recoverable oil reserves within its two Erbil area licenses of 136 million barrels in the Benenan and new Bastora fields.

DNO, which is scheduled to produce development plans for those two fields by the end of the year, said it had also reported to the natural resources ministry that it estimates its three licenses hold a potential of 3.05 billion barrels "in known but undrilled prospects and geological horizons."