NEW ORLEANS—BP's massive oil spill will become the largest ever in the Gulf of Mexico by Thursday based on the highest of the federal government's estimates, an ominous record that underscores the oil giant's dire need to halt the gusher.
The oil that's spewed for two and a half months from a blown-out well a mile under the sea is expected to surpass the 140 million gallon mark, eclipsing the record-setting Ixtoc I spill off
Mexico's coast from 1979 to 1980. Even by the lower end of the government's estimates, at least 71.2 million gallons are in the Gulf.
The growing total is crucial to track, in part because Great Britain-based BP PLC is likely to be fined per gallon spilled, said Larry McKinney, director of Texas A&M University at Corpus Christi's Gulf of Mexico research institute.
"It's an important number to know because it has an impact on restoration and recovery," McKinney said.
The oil calculation is based on the higher end of the government's range of barrels leaked per day, minus the amount BP says it has collected from the blown-out well using two containment systems. Measuring it helps scientists figure out where the missing oil is, hidden below the water surface with some even stuck to the seafloor. Oil not at the surface damages different parts of the ecosystem.
"It's a mind-boggling number any way you cut it," said Ed Overton, a Louisiana State University environmental studies professor who consults for the federal government on oil spills. "It'll be well beyond Ixtoc by the time it's finished."
And passing Ixtoc just before the July Fourth weekend, a time of normally booming tourism, is bitter timing, he said.
The BP spill, which began after the Deepwater Horizon drilling rig explosion killed 11 workers April 20, is also the largest spill ever recorded offshore during peacetime.
But it's not the biggest in history.
That happened when Iraqi forces opened valves at a terminal and dumped about 460 million gallons of oil in 1991 during the Persian Gulf war.
As the Gulf gusher neared the record, Hurricane Alex whipped oil-filled waves onto the Gulf Coast's once-white beaches. The government has pinned its latest cleanup hopes on a huge new piece of equipment: the world's largest oil-skimming vessel, which arrived Wednesday.
Officials hope the ship can scoop up to 21 million gallons of oil-fouled water a day. Dubbed the "A Whale," the Taiwanese-flagged former tanker spans the length of 3½ football fields and is 10 stories high.
It just emerged from an extensive retrofitting to prepare it specifically for the Gulf.
"It is absolutely gigantic. It's unbelievable," said Overton, who saw the ship last week in Norfolk, Va.
The vessel looks like a typical tanker, but it takes in contaminated water through 12 vents on either side of the bow. The oil is then supposed to be separated from the water and transferred to another vessel. The water is channeled back into the sea.
But the ship's never been tested, and many questions remain about how it will operate. For instance, the seawater retains trace amounts of oil, even after getting filtered, so the Environmental Protection Agency will have to sign off on allowing the treated water back into the Gulf.
"This is a no-brainer," Overton said. "You're bringing in really dirty, oily water and you're putting back much cleaner water."
The Coast Guard will have the final say in whether the vessel can operate in the Gulf. The owner, shipping firm TMT Group, will have to come to separate terms with BP, which is paying for the cleanup.