Oil giant BP is fighting charges that it violated probation for a 2006 oil spill on Alaska's North Slope by allowing another large spill in the area three years later.
The Anchorage Daily News said BP pleaded not guilty on Monday to probation violations related to a criminal conviction for the 2006 North Slope oil spill. The company has been on probation since it pleaded guilty to violating the US government's Clean Water Act for that spill.
Federal prosecutors say BP breached its probation when it spilled about 13,000 gallons of oil on to the tundra at the Lisburne oil field in 2009.
BP Alaska spokesman Steve Rinehart said the company had met all the terms of its 2007 plea agreement and did not need to remain on probation.
In the meantime the company agreed to abide by the terms of its probation while the case proceeded in federal court. Probation had been set to expire on November 28.
If BP is found guilty, it could face five additional years of probation and a 12 million-dollar (£7.7m) fine, assistant US attorney Aunnie Steward told a federal magistrate judge in Anchorage.
In 2006 more than 200,000 gallons of oil leaked on to the tundra in what turned out to be the largest oil spill on the North Slope. The spill was blamed on neglect and a corroded pipe.
BP's 2007 plea agreement included three years of probation and 20 million dollars (£12.9m) in fines and restitution. While smaller, the 2009 spill in the Lisburne field was also one of the North Slope's largest spills.
The company's probation officer, Mary Barnes, filed a petition to revoke probation in November. She said BP broke its probation when it failed to take action on warning signs that the Lisburne pipeline was compromised months before it leaked.
Mr Rinehart said the 2009 spill should be viewed in the context of the significant improvements the company had undergone to make the Prudhoe Bay operation safer. A decision on whether BP will remain on probation is up to US District Judge Ralph Beistline. He has not yet scheduled a hearing.