Russian oil giant Rosneft has signed a deal with Norway's Statoil to explore the sea around the Arctic.
It is the third deal Rosneft has signed in the past month, after Arctic exploration agreements with Italy's Eni and US giant Exxon Mobil.
Norway's state-held firm will get ownership of a third of a new joint venture that will explore one of Rosneft's fields in the Barents Sea.
The deals are a sign of Rosneft's growing global ambitions.
The Statoil agreement also covers three Rosneft blocs in the Far Eastern Sea of Okhotsk.
Some media reports put the value of the deal at about $2.5bn (£1.5bn) but Statoil told the BBC that it has "not given any valuation of the deal".
"Pending results further exploration wells could be drilled, and if we are successful in making discoveries there will be substantial investments for developments," Statoil spokesman Bard Glad Pedersen said.
The deal was signed by the two companies' chief executives in the presence of Russian Prime Minister Vladimir Putin, who will return to the presidency in a few days' time.
"We value our relations with our neighbours and are confident that the project will develop well," Mr Putin said.
"There is no question that it will not have the government's full support."