Statoil said it produced around 7,500 barrels of oil per day during a test at a production well on the Gullfaks A platform. Based on preliminary calculations, Statoil said the discovery may hold 40 million-150 million recoverable barrels of oil equivalent.
Statoil Vice President Oystein Michelsen said the latest find at Gullfaks was "a result of Statoil's strategy for revitalization of the Norwegian continental shelf."
Statoil said the reserve estimate came with a high degree of uncertainty, though nearly 1 million barrels of oil was produced in nearby formations since December 2012.
Gullfaks came online in 1986. Three permanent installations there have netted more than 2.4 billion barrels of oil and more than 1.9 trillion cubic feet of natural gas from the entire complex for Statoil.
The company said parts of the field were closed in 2008 in order to maintain pressure levels at the site for future drilling operations. Pressure in mature fields like Gullfaks declines as production occurs.
Statoil announced plans last year to boost recovery at its parts of the field through a $1.4 billion investment.