On Monday afternoon, BP reported that it was capturing about 11,000 barrels per day of the oil that has been spilling into the Gulf of Mexico since the Deepwater Horizon drilling rig sank on April 22.

The siphon is one of the first positive developments since the disaster began, but, as we wrote last week, there’s still no reason for reporters to be lulled into complacency by techno-optimism. Indeed, three days after we warned against having too much faith in “mechanical Band-Aids,” New York Times blogger Andrew Revkin wondered:

Now that about half* of the gushing oil is being siphoned to a ship, will we forget that such deep-water blowouts are probably uncontrollable, as explained in 1997? It would be a shame if a Band-Aid fix on a petro-calamity led to a more relaxed view of such risks.

The asterisk in that paragraph is important, and Revkin points out in the accompanying footnote that the “about half” reference is subject to major uncertainty. The reason is that we still don’t know exactly how much oil is spewing out of the well every day, especially since BP cut the riser pipe from which the crude was spilling in order to attach a cap for the siphoning work. As a front-page New York Times story pointed out on Monday:

A federal panel has estimated that 12,000 to 25,000 barrels a day is flowing from the well. But those calculations were made before BP cut the riser pipe last week to accommodate the capping device, which administration officials have said could increase the flow rate by as much as 20 percent.

On his True Slant blog, freelance investigative reporter Osha Gray Davidson criticized BP’s “kinky math,” reasoning that “the 10,500 barrels [BP is now siphoning to the surface] can’t simply be subtracted from the estimated flow at the well head.” Because cutting the pipe may have increased the spill’s flow by 3,800 barrels per day and because the new siphon replaced an old one that was already capturing to 2,000 barrels per day, the company was, as of Sunday, capturing a “net gain” of only 4,700 barrels of oil per day.

Math tends to intimidate reporters, but such back-of-the-envelope calculations are a great check on unwarranted techno-optimism, especially given BP’s many dodges and feints since the oil spill began. Take the company’s failed effort to plug the well using a “top kill” procedure, which shot heavy drilling mud and bits of rubber down the hole. Many news outlets explained that the success of this approach hinged on overcoming the pressure of the oil and gas coming up the well, but few reporters bothered to ask how much pressure BP was dealing with. One was the Los Angeles Times’s Amina Khan, who did an exemplary bit of legwork in order to report that:

Success of the [top-kill] venture will depend on loading enough mud and cement into the well to stop the surge of oil and gas — a tricky proposition. Iraj Ershaghi, director of the petroleum engineering department at USC, estimated that the upward pressure was likely to be about 9,000 pounds per square inch. At a depth of 5,000 feet, the water pressure bearing down on the leak is about 2,500 pounds per square inch, he added.

That leaves a difference of about 6,500 pounds per square inch of upward pressure at the wellhead, explaining why the oil and gas flowing upward can easily overwhelm the water pressing down on it and why the crude has continued to gush into the ocean.

“This is not a kids’ game, to fight that kind of pressure,” Ershaghi said..

Had more reporters looked for somebody to help them with that simple calculation before the top-kill failed (as Khan did, filing her story on May 25), they might not have been so willing to accept BP’s disingenuous early assurances that the effort was going just fine.

Unfortunately, math continues to be a major stumbling block for journalists covering the spill, and that must change. With a little number crunching they could do a lot to fight back against more false promises.

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Curtis Brainard is the editor of The Observatory, CJR's online critique of science and environment reporting. Follow him on Twitter @cbrainard.