The additional resources, most of which are natural gas, amount to around 2.5 billion barrels of oil equivalent (boe), according to the Norwegian Petroleum Directorate.
The increased reserve estimates follow the 2011 signing of an agreement between Norway and Russia on their maritime border in the Barents Sea after a 40-year dispute, granting the Scandinavian country an area covering some 44,000 square kilometres.
A seismic survey carried out since then estimated the resources in the once disputed part of the Barents at 1.9 billion boe, out of which 15 percent could be oil, the agency said.
The new estimates also included the waters around the Jan Mayen island, 500 kilometres east of Greenland, but uncertainty was higher there due to less detailed knowledge of the area, it said.
The Norwegian Petroleum Directorate said the Jan Mayen area could hold 566 million boe, but also substantially more -- or nothing at all.
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Norway is one of the world's biggest exporters of oil and gas. In January, it produced 1.473 million barrels of oil per day and sold 10.5 billion cubic metres of natural gas.