* Says finds 100 million to 400 million barrels off Norway
* Total formation could hold far more, says Det norske
* Could be first giant North Sea find "in many, many years"
* Lundin shares jump 18 percent on news of discovery
By Walter Gibbs and Gwladys Fouche
OSLO, Sept 17 (Reuters) - A Norwegian oil discovery announced on Friday by Sweden's Lundin Petroleum may be the biggest one off Norway in years, Norwegian oil company Det norske said.
Det norske Senior Vice-President Odd Ragnar Heum said the geology around Lundin's oil strike west of Norway indicated there was lots more oil in nearby acreage, where Det norske and several other companies have exploration licenses.
"If you include the unproven potential reserves in the neighbouring licenses where we are partners, you could easily see 500-600 million barrels in recoverable volume," Heum told Reuters.
That would make it "the first giant oil discovery in the Norwegian part of the North Sea in many, many years," he said.
Lundin estimated the find in its license area, called Avaldsnes, contained "recoverable resources of 100-400 million barrels of oil equivalent."
Shares in Lundin jumped 17.75 percent to 55.60 Swedish crowns at 1551 GMT, outperforming a 0.5 percent rise on Stockholm's OMX S30 index.
Lundin shares the license there with Norway's Statoil and Denmark's Maersk Oil.
Heum told Reuters the column of oil in Lundin's area measures 17 metres from top to bottom, and that it likely becomes deeper in a neighbouring block identified by Norwegian authorities as PL 265.
The operator of that block is Statoil, while state-owned Petoro owns a 30 percent license interest, Det norske owns 20 percent and Lundin 10 percent, according to the Norwegian Petroleum Directorate (NPD).
Statoil and Lundin declined to comment on Heum's description of the extent of the discovery.
A third block that Det norske says may contain oil is also operated by Statoil, with Petoro and Det norske as additional licensees, according to the directorate.
Lundin said in a statement that appraisal wells will be required "to fully delineate the structure" in its area.
Heum said the licensees in the adjacent areas would undertake their own appraisals.
"In the end there will be a unitization," he said, "which means the ownership will be calculated and distributed across the whole field."
In a statement, the NPD commented only on Lundin's initial find. "Preliminary estimates of proven recoverable oil are 15 million standard cubic metres (Sm3) with an upside of about 60 million Sm3, which will require further delineation in the production licence," it said.
Those cubic-metre figures translate to a preliminary estimate of 94 million barrels of recoverable oil, with an upside of 377 million barrels, slightly less than Lundin itself reported.
Oil production on the Norwegian continental shelf peaked in 2001 and has declined by almost a third since then, to 2.13 million of barrels a day in 2009.
Increased gas production has partly made up for the decline in oil revenues, but Norwegian leaders have been preparing for leaner budgets in future as the North Sea oil age wanes. (Editing by James Jukwey)