* Gas output cut by 21 mcm/day Friday, also cut on Saturday
* Prior to incident, March output estimated at 116,000 bpd
* Unclear when output will resume
OSLO, March 15 Output at the Oseberg oil and gas field in the North Sea is shut after multiple power failures and gas leaks, and the situation remains unstable, Statoil and the country's safety regulator said on Friday.
"Oil and gas production remains shut down. Crews are working hard to restore stable main power supply on board so that ... personnel can be taken on board and activities resume," Statoil said on its website on Friday.
Oseberg is one of the four fields that help establish the Brent oil benchmark.
The first power failure occurred around 1600 GMT on Thursday at the Oseberg B platform, shutting production down.
At 1650 GMT a gas leak was detected, causing staff to run for the lifeboats. At around 1730 GMT the leakage was stopped and power restored.
At 0015 GMT on Friday another gas leak was detected, this time at the Oseberg A platform, but that situation was soon resolved. Another power cut occurred later, however.
Before the outage, Oseberg's oil output was estimated to reach 116,000 barrels per day in March and 120,000 bpd in April, according to loading schedules compiled by Reuters.
Gas output at Oseberg was cut by 21 million cubic metres per day on Friday, North Sea infrastructure operator Gassco said on Friday.
"There will also be a smaller reduction for (Saturday)," it said on its website.
Oseberg is located in the northern part of the North Sea and consists of two facilities, the process and accommodation facility Oseberg A and the drilling and water injection facility Oseberg B.
"We still have an unclear situation, but it is less serious than we thought at first," said Inger Anda, a spokeswoman for the Norwegian oil safety regulator.
The Petroleum Safety Authority Norway graded the incident at a 2 on a scale of 1 to 5, where 1 is the least serious and 5 the most serious incident.
"We will be following the situation over the weekend, especially concerning what happened on Oseberg B," Anda added. "We always look very seriously at a gas leak at a producing installation."
Close to 700 people work at the offshore centre, Statoil said.
Oseberg, which last year was Norway's eighth-biggest oil producing field and its fifth-biggest gas producer, also processes oil and gas from the fields Oseberg Oest, Oseberg Soer and Tune.
The partners in the Oseberg field are Statoil (49.30 percent), Total (10 percent), ExxonMobil (4.70 percent), ConocoPhillips (2.40 percent) and Norwegian state-owned firm Petoro (33.60 percent).