Since 2000, BP has been fined and criticized for cutting corners and not properly maintaining Prudhoe Bay. BP operates the Alaska oil field on behalf of itself, ConocoPhillips, Exxon Mobil Corp. and other companies. Here's a timeline of BP's issues at Prudhoe Bay:
2000: BP is placed on five years federal probation, stemming from an incident in which a contractor dumped thousands of gallons of toxic material underground at a BP oil field in Alaska during the 1990s. BP pleads guilty to a single felony in connection to the incident, admitting that it took too long to notify federal regulators about the dumping. It pays a $6.5 million fine and agrees to set up a nationwide environmental management program, which ultimately cost about $40 million.
2001: A work crew injects oil and fluids underground to dispose of them after a small spill. BP pays $675,000 in fines for not consulting with state environmental regulators before dumping the material.
Spring 2001: Alaska regulators discover that safety valves atop of some Prudhoe oil wells, which shut down production if pressure drops because of a leak, have high failure rates, prompting regulators to step up inspections and call on BP to do a better job of inspecting wellheads.
Fall 2001: Responding to whistleblower complaints, BP conducts an internal audit and releases the results, which find some employees are concerned about Prudhoe staff cuts, maintenance backlogs and other problems that could threaten operation of the field. Workers believe "management's top priority is controlling costs and achieving short-term budget targets," not safety and regulatory compliance, according to BP's audit.
January 2002: BP replaces a faulty valve used to isolate oil and gas leaks at Prudhoe Bay, a move that comes nearly four years after its workers first asked the company to fix the problem following a 1,200-gallon oil spill. Workers took it upon themselves to test the valve to convince BP managers that it leaked dangerously.
June 2002: Alaska regulators fine BP up to $300,000 for taking too long to install a sensitive system to detect leaks from Prudhoe Bay's huge oil trunk lines. BP was supposed to comply with the law by 1997, yet was still behind schedule in mid-2002.
August 2002: An explosion at a Prudhoe Bay oil well house seriously injures a worker. Regulators say BP allowed excessive pressure to build up in the well. The company pays more than $1.2 million in fines.
December 2002: Responding to worker accusations that BP broke its federal probation, a federal judge orders the company to allow BP's probation officer unrestricted access to its oil facilities and records to verify it is in compliance with environmental and safety laws.
2004: The head of the Alaska Department of Environmental Conservation tells the EPA that BP hasn't complied with its federal agreement stemming from its probation.
2005: BP announces it will spend more than $140 million to refurbish 70 oil wells at Prudhoe Bay, part of a company effort to update equipment at the aging oil field.
March 2, 2006: A worker at Prudhoe Bay spots the frozen tundra drenched with some 20o,000 gallons of oil. Unbeknownst to BP, one of the company's transit pipelines had become corroded and was leaking for days, resulting in the biggest spill ever recorded in an Alaska oil field. A pipeline detection system failed to catch the leak.
Aug. 6, 2006: BP temporarily shuts down half of Prudhoe Bay after discovering another corroding, leaking pipeline. The company admits it has not used an electronic "pig" — a device that cleans and monitors the inside of pipelines — on the trunk line in years, even though some workers suspected sludge buildup and corrosion. In the aftermath, BP announces it will replace 16 miles of worn pipeline at an estimated cost of $170 million. In the following months, federal and state regulators launch investigations and congressional hearings are held.
Nov. 29, 2007: BP is put on three years' criminal probation in connection with the 2006 oil spills. The probation settles a misdemeanor charge brought under the Clean Water Act.
March 2009: Both the state and federal governments file civil lawsuits against BP over the 2006 spills. The state case, which is still pending, aims to collect back taxes and fines as a result of revenue that was lost when the trans-Alaska pipeline was shutdown while the leaking lines were repaired. The federal case seeks penalties for violations of the Clean Water Act, the Clean Air Act and failure to comply with corrective action orders from the federal Pipeline and Hazardous Materials Safety Administration.
Nov. 9, 2009: An 18-inch flow line ruptures at BP's Lisburne field, spilling nearly 50,000 gallons of an oil and water mix onto the tundra about half a mile from Prudhoe Bay. Warnings, including sensors that showed drops in temperature and even alarms, began going off but BP operators failed to investigate or troubleshoot the cause of the alarms for months.
November 2010: The federal probation officer supervising the criminal case stemming from the 2006 spills asks that BP's probation be revoked based on the company's behavior in the 2009 Lisburne pipeline rupture. A hearing is set for Sept. 6, 2011 in that case.
May 3, 2011: The federal government and BP announce a settlement in the federal civil case relating to the 2006 Prudhoe Bay spills. If approved by the court after a 30-day public comment period, BP will pay a $25 million fine and comply with detailed pipeline monitoring and safety requirements. Federal officials say it is the largest per-barrel fine ever levied in a U.S. oil spill.
Nov. 29, 2011: Federal prosecutors will ask a judge to place BP on probation again, this time in connection to the Nov. 9, 2009, oil spill.