Norwegian Petroleum and Energy Minister Odd Roger Enoksen has resigned, the prime minister's office said on Friday without naming his replacement.
Earlier Norwegian broadcaster NRK reported that Enoksen would step down to make room for the leader of his Centre Party, Aaslaug Haga, to take the high profile post.
The government statement did not say why Enoksen had resigned but said that it was his decision. Prime Minister Jens Stoltenberg will hold a news conference at 10.15 London time.
The oil minister's job is one of the most important cabinet posts in Norway, which is the world's fifth biggest crude exporter and Western Europe's biggest natural gas exporter.
Enoksen has overseen preparations to merge the oil and gas activities of Norsk Hydro with bigger rival Statoil by the end of September to form a powerful Norwegian energy group better able to compete abroad.
The Centre Party, a frequent king-maker in Norwegian politics, has often held the post of energy minister.
Haga, who has been Minister of Local Government and Regional Development in the Labour-led coalition government, will be succeeded by another Centre Party MP, NRK said.