OSLO, Norway — When Statoil acquired the last of three licenses off Greenland’s west coast in January 2012, oil at more than $110 a barrel made exploring the iceberg-riddled waters an attractive proposition.

Less than two years later, the price of oil had been cut by almost half. Norway’s Statoil, the world’s most active offshore Arctic explorer in 2014, relinquished its interest in all three licenses in December without drilling a single well, a spokesman for the state-controlled company said by email.

Statoil’s decision shows how the plunge in oil, with Brent crude trading at about $45 a barrel, has dealt another blow to companies and governments hoping to tap the largely unexplored Arctic. That threatens to demote the importance of a region already challenged by high costs, environmental concerns, technological obstacles and, in the case of Russia, international sanctions.

“At $50, (exploration) just doesn’t make sense,” James Henderson, a senior research fellow at the Oxford Institute for Energy Studies, said Monday in a phone interview. “Arctic exploration has almost certainly been significantly undermined for the rest of this decade.”

RICH RESERVES, SLOW PROGRESS

The Arctic – spanning Russia, Norway, Greenland, the U.S. and Canada – accounts for more than 20 percent of the world’s undiscovered oil and gas resources, including an estimated 134 billion barrels of crude and other liquids, and 1,669 trillion cubic feet of natural gas, according to the U.S. Geological Survey. That’s almost as much oil as Iraq’s proven reserves at the end of 2013 and 50 percent more gas than Russia had booked, BP Plc’s Statistical Review of World Energy shows.

Yet explorers seeking a piece of the Arctic prize have been tripped up for years.

After spending $6 billion searching for oil off Alaska over the past eight years, Royal Dutch Shell asked in October for an extension of licenses, as setbacks such as a stranded oil rig and lawsuits risk further delays in drilling. Cairn Energy spent $1 billion exploring Greenland’s west coast in 2010 and 2011 without making commercial discoveries, and Gazprom has shelved its Shtokman gas field in the Barents Sea indefinitely because of cost challenges.

Environmental group Greenpeace has occupied oil rigs from Norway to Russia, arguing that a spill would cause irreparable damage to ecosystems that sustain animals from polar bears to birds and fish. The possibility that economically marginal fields such as Arctic deposits might be stranded as governments adopt stricter climate policies also has shaken some investors.

As oil companies cut spending to cope with falling prices, already costly and risky Arctic projects will fall down the priority list even if crude prices are expected to recover by the time production starts, Henderson said. Global capital expenditures will probably drop by more than 20 percent this year, according to a Jan. 9 note from Sanford C. Bernstein.

HOLD ON INVESTMENTS LIKELY

Like Statoil, Dong Energy A/S and GDF Suez have returned Greenland licenses because exploration has become too expensive, the Danish newspaper Politiken reported.

Statoil, which cut spending plans to boost shareholder returns even before oil prices started to fall last year, last week signaled it could delay the flagship Johan Castberg project in Norway’s part of the Barents Sea for a third time as it struggles to find a profitable development solution. Even if the Barents Sea enjoys a milder climate than other parts of the Arctic because of the Gulf Stream, it remains a remote region with little infrastructure and logistics for use by Statoil, the same company that planned to build a major wind farm off Maine’s coast, but pulled the plug in 2013 after political maneuvering by Gov. Paul LePage.

“Investment decisions on developments are very unlikely in the next two years,” said Erik Holm Reiso, a partner at Oslo-based consultant Rystad Energy AS. In most of the Arctic, “exploration will be sporadic,” he said.