The United States Coast Guard is demanding an end to a 14-year oil spill that has dumped as much as 3.5 million barrels of crude oil into the Gulf of Mexico since 2004, putting it on track to surpass the Deepwater Horizon disaster as the country’s worst spill ever.

The Coast Guard issued its cleanup order on October 24, the day after the Washington Post published an exposé on the spill.

If New Orleans-based Taylor Energy refuses to contain the spill and clean up after itself, it will face fines of US$40,000 per day, the Post reports.

“Up to 700 barrels of oil per day have leaked from Taylor Energy’s former site 12 miles off the coast of Louisiana since the platform was destroyed during Hurricane Ivan in 2004,” the paper notes, citing U.S. Justice Department data. “The spill so far amounts to at least 1.5 million barrels and up to 3.5 million barrels. That would rival the BP Deepwater Horizon disaster, the largest offshore spill in the nation’s history, which spewed four million barrels of oil into gulf waters.”

The Justice Department commissioned the geoscience assessment after the company demanded the government “return more than $400 million placed in a trust to pay for plugging the wells and cleaning the site.”

Taylor has capped nine of the 28 wells at its offshore platform and disputes the government data, claiming the “deeply-flawed analysis and inflated volumes” are no more than a legal tactic. But the company basically admits there’s nothing it can do to curtail the spill.

“Taylor Energy’s greater concern is that the government is leading the response down a dangerous path that will create an environmental impact that currently does not exist,” the company said in an official statement. “If there were anything legally permissible and effective that Taylor Energy could do in an environmentally responsible manner to stop the sheen, we would have already done it.”

But Oscar Garcia-Pineda, the geoscientist hired by Justice, was just as scathing about the earlier Coast Guard estimates based on company data. “There is abundant evidence that supports the fact that these reports…are incorrect,” he wrote. “My conclusion is that [the Coast Guard] reports are not reliable.”

Out on the gulf, “the Taylor site’s rainbow-coloured oil slicks are often visible for miles, and the broken wells release so much oil that researchers have needed respirators to study the damage,” the Post reports.

The spill “was hidden for years as the company and the Coast Guard declined to inform the public that it existed. Environmental groups that monitor the gulf were unaware that the broken wells were leaking for six years—until the catastrophic BP Deepwater oil spill in April 2010.” The Gulf Restoration Network and SkyTruth, a non-profit remote sensing group “stumbled upon oil slicks that were unrelated to the Deepwater Horizon site,” traced them back to Taylor, and called the Coast Guard.

“It was there all the time, longer than the BP spill,” said SkyTruth founder and president John Amos.