Oct. 22 (Bloomberg) -- An oil spill from a leaking well off Western Australia may have polluted the Timor Sea with 10 million liters, about 63,000 barrels, of oil, making it among the three worst in the country’s history, the Greens said today.

The Montara well may be spilling as much as 3,000 barrels of oil a day, Greens Senator Rachel Siewert said in a statement, citing information sourced by the party. That’s up to 10 times higher than the estimate from field operator PTT Exploration & Production Pcl, which puts the flow at about 300 to 400 barrels a day, spokesman Mike Groves said by phone today.

Bangkok-based PTTEP is due to make a fourth attempt tomorrow to intercept the leak, 2,600 meters (1.6 miles) below the seabed, in an effort to plug it. Oil, gas and condensate began seeping into the Timor Sea from the well on Aug. 21. The opposition Liberal Party has called on the government to intervene in the operation should the next bid fail.

Australia’s department of resources, energy and tourism has calculated the well is leaking oil at a rate of 2,000 barrels a day, based on data from Geoscience Australia, the Greens said. The estimate was made by department officials at a Senate hearing in Canberra yesterday, Siewert said.

Australia’s most-severe recorded spill was when the tanker Kirki lost its bow off the coast of Western Australia in 1991, leaking about 17,280 tons of light crude into the sea, according to the Australian Maritime Authority’s Web site. The Princess Anne Marie lost 14,800 tons off Western Australia in 1975 after a crack to her hull. A spill of 10 million liters, as estimated by the Greens, would be about 8,800 tons. PTTEP spokesman Groves declined to comment on the figures.

Humpback Whales

The Montara well is in water 83 meters deep and some 690 kilometers from Darwin in the Northern Territory and 250 kilometers from Truscott on Australia’s northwestern Kimberley Coast.

The world’s largest population of humpback whales, estimated at about 1,000, is found along the Kimberley Coast, ABC News reported today, citing an aerial and sea-based survey. Tourism Australia has described region as “one of the world’s last true wilderness areas.”

About 300 people are working on addressing the spill, in the Timor Sea, at the Truscott air base and at Darwin, PTTEP has said. Seventeen vessels and nine aircraft, including a Boeing 747, have been used in the operation since Aug. 21.

The cost of the cleanup has reach A$5.3 million ($4.9 million), a Senate hearing heard this week. PTTEP has said it will pick up the bill for the operation.

By Oct. 20, 457,000 liters of oil product, including 277,000 liters of oil, had been removed from the ocean, the marine safety authority said. Aerial surveillance shows oil about 201 kilometers from the Western Australian coast and 257 kilometers off Indonesia, it said. The oil currently poses no threat to environmentally sensitive reef areas, the authority said Oct. 21.

PTTEP has drilled a relief shaft at the Montara field to intercept the leaking well and plug it, and intends to halt the flow by injecting heavy mud.

To contact the reporter on this story: Ben Sharples in Melbourne at bsharples@bloomberg.net

Last Updated: October 21, 2009 21:57 EDT