How much oil has gushed into the Gulf of Mexico from Macando/Deepwater Horizon?

This is a basic element of understanding the gigantic science experiment known as the BP oil disaster. It's inevitable that BP and its Republican defenders will play all sorts of games with the numbers.

One of the complications of this is that the liquid volume of a barrel isn't always the same: "In the U.S. Customary System it varies, as a liquid measure, from 31 to 42 gallons (120 to 159 liters) as established by law or usage." Yahoo! Education) The estimated amounts are sometimes given in news reports in barrels, sometimes in gallons.

The University of North Carolina at Chapel Hill site How Many? A Dictionary of Units of Measurement (2001) defines "barrel" as follows:

a commercial unit of volume used to measure liquids such as beer and wine. The official U. S. definition of the barrel is 31.5 gallons, which is about 4.211 cubic feet or 119.24 liters. This unit is the same as the traditional British wine barrel. In Britain the barrel is now defined to be 36 Imperial gallons, which is substantially larger: about 5.780 cubic feet or 163.66 liters. This unit is slightly smaller than the traditional British beer and ale barrel, which held 5.875 cubic feet or 166.36 liters. There are other official barrels, defined in certain U.S. states; most of them fall in the general range of 30-40 gallons. A barrel of beer in the U.S., for example, is usually 31 U.S. gallons (117.35 liters).

Then there is this definition from Dictionary.com (my emphasis):

the quantity that such a vessel of some standard size can hold: for most liquids, 31 1 / 2 U.S. gallons (119 L); for petroleum, 42 U.S. gallons (159 L); for dry materials, 105 U.S. dry quarts (115 L).

Sizes.com agrees, but adds a wrinkle (my emphasis):

The barrel of petroleum, 1866 – present, a unit of capacity = 42 U.S. gallons (or about 5.61458 cubic feet, and though approximately 158.987 liters is taken as = 159 liters, by, for example, the U.S. Census Bureau Harmonized System), measured at a temperature of 60° Fahrenheit. It is a unit of account; actual barrels containing 42 gallons of crude oil have not been used for more than a century, if ever.

So, until further enlightened, I'm going to assume 42 gallons per barrel when I'm seeing these measurements of the Gulf oil. The following are some recent reports, with my emphasis in bold:

Curtis Morgan, When will oil spill be cleaned up? Maybe never 07/30/2010:

Yet even combining natural forces with months of burning, skimming and siphoning, the most optimistic estimates suggest tens of millions of gallons remain in the Gulf. It could be soaked into unsurveyed marshes, adrift in countless gobs too small and scattered to show up in satellite images or — most concerning — still under water.

Much of what remains will likely be difficult, or impossible, to capture or clean up.

Bruce Nichols and Deborah Zabarenko, BP prepares to plug Gulf oil well for good Reuters 08/01/2010:

The well has been temporarily sealed for two weeks after spilling up to 60,000 barrels a day since April, when an oil rig explosion killed 11 workers and triggered the leak.

Sixty thousand barrels a day for 100 days at 42 gal/bbl would be 252 million gallons.

Bob Marshall, Surface of Gulf of Mexico looks better, but millions of gallons of oil remain below New Orleans Times-Picayune 07/29/2010:

For months a fleet of research vessels has been tracking clouds of diffused oil particles floating 3,300 to 4,300 feet below the surface, said Steve Murawski, NOAA's chief scientist for fisheries. The microscopic droplets were formed when the dispersant Corexit was pumped into the geyser of oil and methane that for 84 days rocketed into the Gulf from the failed wellhead 5,000 feet below the surface.

"These are tiny droplets, between 20 and 60 microns, and with the concentrations we're seeing (4 to 5 parts per million) when you put this in a beaker it looks like clear sea water," Murawski said. "You can't see it, but there's definitely components (of the oil) in the water." ...

"The confusion comes with the word 'oil' itself," he said. "Most people hear 'oil' and they think of the dark, gloppy stuff that comes in the can at the automotive store, or from the barrels in Saudi Arabia.

"But oil is composed of many, many more components than the black stuff you see. And when that black stuff is gone, there's still plenty of those components -- many of which are extremely toxic -- still in the water."

Rader, like other marine scientists, is concerned the public will lose interest in the threat posed by the disaster once the surface is clear.

"If you go back and look at the sheer amount of oil dumped -- 60,000 barrels a day for 87 days -- you get about 220 million gallons," he said. "Of that, 11 million gallons were burned and 30-some million were collected, meaning about 50 million gallons were eliminated.

"That leaves you about 175 million gallons of oil-based pollution loose in the Gulf. And when it degrades from the thick stuff you can see, that doesn't mean it's all gone. There's still an untold amount of toxins from that oil in the marine environment."

Curtis Morgan, Recovery in the Gulf: A test of technology, nature and time Miami Herald 07/31/2010:

Take 100 to 200 million gallons of light sweet crude. Add two million gallons of industrial solvents and trade-secret chemicals. Blend 5,000 feet below the ocean surface. Spread across fragile estuaries and rich ocean waters. Stew in hot sun and hungry bacteria for three months. As a finishing touch, whip lightly in a tropical depression. ...

"The sheer volume of oil that's out there has to mean there will be some very significant impacts," said Jane Lubchenco, administrator of the National Oceanic and Atmospheric Administration, which has a team calculating an "oil budget" intended to narrow down how much remains unaccounted for and where it might be.

But a crude calculation, based on the estimated spill minus the oil cleaned up and biodegraded, would put the unaccounted-for amount at anywhere from 50 million to 115 million gallons.

George Prentice, BP lawsuits over oil spill take center stage Reuters 07/29/2010:

Millions of gallons of oil leaked into the ocean over nearly three months -- until the well was capped two weeks ago.

Katarzyna Klimasinska, BP to Begin Permanent Plugging of U.S. Gulf Well Bloomberg Business Week 08/01/2010:

Before being sealed last month, Macondo [Deepwater Horizon] was spewing 35,000 to 60,000 barrels of crude into the Gulf, according to a government estimate released in June. Allen said July 30 that the government will release a new estimate within a few days for the amount of oil that was leaking into the Gulf, as well as for how much oil has been dispersed.

BP will owe fines on the amount of escaped oil, so they have a financial as well as public relations incentive to minimize the officially estimated amount.

Curtis Morgan and Fred Tasker, Gulf oil spill: 100 days, 10 lessons Miami Herald 07/29/2010:

For weeks after the April 20 spill, BP was estimating the flow of oil at 5,000 to 20,000 barrels a day, and responded with a "top hat" containment device capable of sucking up only about 15,000 barrels a day. But by mid-June government scientists were saying the well was spilling 50,000 barrels a day or more, and the Obama administration demanded a bigger, faster response from BP.

Fifty thousand barrels a day for 100 days at 42 gal/bbl would be 210 million gallons.

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