BP could be forced to pay higher penalties over the 2006 Prudhoe Bay oil spill, the worst onshore pipeline leak in Alaska's history, depending on the outcome of a trial under way in Anchorage.
A second spill in the state, in 2009, proves that BP broke its promises to tighten safety procedures, the US government is claiming.
While BP has faced an even bigger financial and legal crisis over last year's Gulf of Mexico oil spill, its earlier problems in Alaska have still not been resolved. A government engineer claimed in court that the oil giant ignored alarms that went off for months which, if checked out, would have prevented the second spill into Alaska's environmentally sensitive frozen wetlands.
Some 13,500 gallons of oil spilled from a ruptured pipeline in November 2009, two years afterBP pleaded guilty to violating the US Clean Water Act at Prudhoe Bay. The Prudhoe Bay spill sent more than 200,000 gallons of crude flooding on to Alaska's north slope, provoking an outcry from environmentalists and disrupting production from the state's largest oil field for several weeks.
BP paid a $20m fine over the incident and was put on criminal probation for three years.
In court papers ahead of the trial, the US government said the 2009 spill was "eerily similar" to the earlier disaster. "BP's 2006 spill was the result of a lack of maintenance and a failure to heed warning alarms indicating that the pipeline was leaking oil," it said. "The 2009 spill vividly demonstrates that BP has not adequately addressed the management and environmental compliance problems that have plagued it for many years."
Matt Goers, an agent for the Environmental Protection Agency, told the court that his investigation into the spill revealed an alarm had gone off 10 times between June 2009 and the spill being discovered that November.
BP says the 2009 spill was an accident rather than the result of negligence. The case is expected to last all week and, if BP loses, the judge could reopen sentencing terms over the earlier spill.