Statoil announced with joint venture partner Exxon Mobil that it discovered at least 4 trillion cubic feet of natural gas offshore in the Tangawizi-1 well. That brings the total reserve estimate to as high as 17 trillion cubic feet, the company said.
"The Tanzania government is pleased to learn about additional gas resources ... and remains optimistic on future developments," Tanzanian Minister for Energy and Minerals Sospeter Muhongo said.
The CIA World Factbook estimates that Tanzania produced more than 2.7 billion cubic feet of natural gas in 2010, the latest year for which estimates are available.
Statoil Exploration Vice President Tom Dodson said Statoil has completed five wells in Tanzania in the last 15 months. More are planned for this year.
Statoil last week reported that a power outage at its offshore Oseberg center in the North Sea led to a natural gas leak, which has since been stopped.
"Oil and gas production remains shut down," the company said. "Crews are working hard to restore stable main power supply on board so that the heating unit can be started, personnel can be taken on board and activities resumed."