Estimate: Spill largest ever on North Slope

? An oil spill discovered earlier this month in Alaska’s Prudhoe Bay was the largest ever on the North Slope, according to an official estimate released Friday.

The estimated spill size of 201,000 to 267,000 gallons far surpasses the 38,000 gallons spilled in 2001, but is much less than the 11 million gallons spilled in Prince William Sound when the Exxon Valdez ran aground in 1989.

The state has kept comprehensive records of oil spills for a decade, with more cursory record-keeping dating to the 1970s, when the trans-Alaska oil pipeline was built.

The estimate was based on a survey conducted this week at the site operated by BP Exploration (Alaska) Inc. where the leak was discovered March 2.

The source of the spill was a quarter-inch hole apparently caused by corrosion inside the three-mile line that leads to the trans-Alaska oil pipeline.