* New well indicates field reaches into a third licence
* Could add 2-3 pct to Sverdrup potential - analyst (Adds detail, analyst, background)
OSLO, March 19 (Reuters) - The giant Johan Sverdrup oil field in the Norwegian North Sea extends into a nearby licence, suggesting it may contain slightly more resources than previously assumed, Statoil said on Tuesday.
The field, Norway's biggest discovery in decades, was already known to lie across two licenses and was estimated to hold up to 3.3 billion barrels of oil.
A new well now indicates it reaches into a third licence where a large oil column was discovered, proving "a small additional upside to the field's resources", Statoil and partner Det norske said.
"They don't provide volumes so it's a little bit speculative," said Thomas Aarestad, an analyst at brokerage Pareto.
"Based on Det norske's earlier estimations of the license ... we're talking about a 2-3 percent additional volume for Sverdrup."
The additional discovery is positive for the firms but could complicate development as the three licences have different ownership structures and firms will have to agree on new stakes.
Statoil, which operates two of the three licences, and Lundin Petroleum, which operates the third, plan further appraisal wells this year and expect a new resource estimate before the end of 2013.
Oil production in Norway, the world's seventh biggest exporter, is expected to fall to a 25-year low this year, but new discoveries like Sverdrup will boost production toward the end of the decade, extending the life of North Sea oil well into the next decade.
In the new discovery in license 502, Statoil has a 44.4 percent stake, state-holding firm Petoro has 33.3 percent and Det norske owns 22.2 percent.
In license 501, Statoil has 40 percent, Lundin 40 percent and Maersk 20 percent. In license 265, Statoil has 40 percent, Petoro 30 percent, Det norske 20 percent and Lundin 10 percent. (Reporting by Gwladys Fouche and Balazs Koranyi; Editing by Mark Potter)