On May 12, one of Shell’s subsea flow lines sprung a leak, and 88,200 gallons of crude oil spilled into the Gulf of Mexico. A Shell helicopter spotted the spill—at that point, roughly the size of Manhattan—floating about 90 miles south of Timbalier Island, Louisiana. By May 16, just three days after cleanup began, Shell and the US Coast Guard declared the case closed. With no oil left on the surface to recover, and no known impacts to wildlife, there wasn’t much more they could do. Are they great at dealing with oil spills these days or what?

Well, of course they aren’t.

You probably haven't heard about this particular oil spill. It's relatively small, falling 11,800 gallons short of the Coast Guard's 100,000-gallon threshold for major spills. But that doesn't mean it's low-impact. Smaller leaks don't just get less press: They get less regulatory oversight, less money for cleanup, and less scientific sampling to determine the spill's environmental effects. And that’s big deal, because this is happening a lot. “This Shell spill is just one of twenty plus we’ve worked on in the last month,” says Doug Helton, operations supervisor for the NOAA Emergency Response Division. “We have dozens to hundreds of these events happening per year, but it’s only the huge ones that get talked about.”

Importantly, even if the spill is high priority, the responsible party—Shell, BP, whoever—is responsible for reporting the spill volume estimate to the government. “We investigate every spill, even if it’s 10 gallons,” said Coast Guard Chief Petty Officer Bobby Nash. "But there’s a dollar amount attached to a spill for the responsible party, and they’ve usually got a pretty good idea of how much is flowing at any given time. We take their initial numbers as a worst case scenario.”

Smaller leaks don't just get less press: They get less regulatory oversight, less money for cleanup, and less scientific sampling to determine the spill's environmental effects.

That's basically like hiring a dingo to babysit your toddler. Fines against oil companies are levied per barrel spilled: $1,100 for negligence, and $4,300 if they’re found guilty of gross negligence. And a gross negligence suit is far less likely to happen if there isn’t significant public interest or an official investigation. Neither of which will happen if the volume estimate was, say, just 11,800 gallons shy of a major spill designation. Not to say that Shell (who declined to comment for this article) intentionally underestimated the volume of this spill. But it certainly would be in any oil company's financial interest—and power—to do just that*.

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The Murky Science of Oil Spill Accounting

The environmental impacts of an oil spill vary hugely, beginning with what kind of oil was spilled. Type 1, like highly volatile gasoline or jet fuel, will evaporate in a day or so. Not so with Type 3 or Type 4 medium and heavy oils—crudes, like the stuff spilled by Shell last month—which stick around and gum up whales’ blowholes.

Location is another huge factor determining response. NOAA’s Emergency Response Division does oceanographic modeling to see how the spill is going to behave. The agency's major concerns are whether the spill will hit the shoreline, a fishery, or a protected area like a wildlife sanctuary. Open ocean spills get far less attention, even though they are far from benign.

Finally, the volume of oil spilled is a whole other kettle of greasy fish. Even impartial observers can have a hard time figuring out exactly how much is floating around. They attempt to do that with the Bonn Agreement Oil Appearance Code, which tells them how thick a spill is based on its (For example, a rainbow sheen is only 0.3 to 5 micrometers thick, where a dark sludge indicates a spill that’s more than 200 micrometers). You can calculate a volume estimate from there. But doing math with swirly, diffusing colors is subjective stuff. And the Bonn Agreement only covers the oil that makes its way to the surface. “If the oil is coming out under high pressure—think about putting your thumb on a garden hose—it's going to be in smaller droplets, and it’ll stay suspended. It can take weeks to months to years to figure out how much was actually spilled,” says Helton.

Even Small Spills Matter

Shell's May spill was basically doomed to obscurity from the start: Ninety miles out into the ocean, 3,000 feet below the surface, and not creeping towards the shoreline nor the nearby Flower Garden Banks marine sanctuary. "It comes back to the ability to provide evidence. If it happens down at the deep there’s no way to do that. Most independent watchdogs don't have the resources to even get out there," says Scott Eustis, a coastal wetlands specialist at the Gulf Restoration Network. "Even the federal government is struggling."

That creates problems on several levels. "Because of the way the spill occurred and because of the lack of infrastructure, there was no scientific sampling at first,” says Ian MacDonald, an oceanographer at Florida State University. “So there’s no way to verify what the degree of impact or potential degree of injury to wildlife was.” Few had the opportunity to corroborate or challenge Shell’s initial volume estimate—which may or may not be the result of a single flyby—and the weather conditions precluded analysis of satellite images.

Pity, because the few people outside Shell who did make it to the site came away deeply concerned. "I was literally knee deep in oil for most of 2010, and I learned from the best," says Jonathan Henderson, founder of environmental watchdog group Vanishing Earth, who flew out on May 14. "This sheen was a deep brown color, which is just raw crude oil. I was very skeptical that there was only 88,000 gallons out there."

It was the distance from shore—and the depth of the spill—that also allowed the Coast Guard and Shell to make statements that there were no known or no reported impacts to wildlife. "Well, who the fuck is going to report it 90 miles out?" Henderson says. MacDonald, who made it to the sheen on the 15th, says he did witness impacted wildlife. "We saw pelagic fish, some seabirds, a pod of porpoises, a beaked whale mother and calf surfacing in and out of the floating oil, schools of fish nearby under the oil," he says.

Beyond the environmental impact of this particular spill, scientists are worried about the cumulative effect of these under-reported spills—especially because methods for cleaning them up are still so limited. The dominant technique, surrounding the oil with booms and skimming it up, “recovers maybe 20 percent of the oil on the surface, and often less than that," says Tim Donaghy, senior research scientist at Greenpeace. Booming and skimming the Shell spill recovered 84,000 gallons of oily water. But that still leaves unanswered exactly how much oil was out there to begin with. Well, maybe not totally unanswered, depending on who you choose to listen to.

*Even during the Deepwater Horizon disaster, BP was forced to quintuple its estimate of the wellhead's daily flow rate from 1,000 barrels to 5,000 barrels—not because of a government investigation and reassessment, but because of satellite and radar data collected by a tiny, independent nonprofit called SkyTruth.