LONDON -- British oil company BP PLC confirmed Thursday that it had received a subpoena from a U.S. grand jury investigating a massive oil leak in Alaska.
BP blamed the incident at Prudhoe Bay field in March on a small hole caused by corrosion in a pipeline. It was the largest spill ever on the North Slope.
"We are fully cooperating with the investigation and we are carrying out our own investigation into what caused the corrosion," BP spokesman David Nicholas said. "We believe that our actions were at all times proper."
Up to 267,000 gallons were believed to have spilled onto the frozen ground from a 34-inch-diameter pipeline in the tundra about 250 miles above the Arctic Circle.
The arctic-grade carbon-steel pipe, which leads eventually to the trans-Alaska pipeline, lies above ground but is covered by a layer of gravel as well as the snow.
BP discovered and plugged the leak on March 2.
A report prepared by a team of BP and state investigators found that a pipeline leak-detection system sounded warnings on four straight days in the week leading up to the spill but field workers interpreted the signals as false alarms.
The report said the leak went undetected for at least five days "and probably much longer."
A grand jury investigation could lead to criminal charges and ultimately fines and prison sentences.
BP is also facing a probe and victims' lawsuits over a March 2005 explosion at its plant in Texas City, Texas, that killed 15 people. The company was fined $21.3 million by the U.S. Occupational Safety and Health Administration for 300 violations.
OSHA said earlier this year the investigation had been referred to the Justice Department for possible criminal prosecution. Justice officials have so far declined to comment.
