Norwegian oil firm Det norske has lifted the resource estimate for the Ivar Aaasen field in the North Sea after signing an agreement to combine several adjunct licenses and good drilling results, it said on Monday.

The firm said the combined estimated gross proven and probable reserves were now 210 million barrels of oil equivalents (mmboe), up 35 percent compared to the end-2013 estimate.

Meanwhile, investments for the field's development were unchanged at 27.4 billion Norwegian crowns ($4.45 billion), it added. The field was still expected to start up production in the fourth quarter of 2016.

Det norske is the operator of Ivar Aasen with a stake of 34.8 percent. Its partners include Statoil, Lundin Petroleum, OMV, Bayerngas, Wintershall, a unit of chemicals giant BASF and VNG.

(Reporting by Nerijus Adomaitis, editing by Gwladys Fouche)