It was July of 2010, more than a week after the final plugging of a calamitous oil leak near the Deepwater Horizon drilling rig, and a sense of confusion was quickly spreading throughout the scientific community. An estimated 4.2 million barrels had spilled into the Gulf of Mexico from an oil well. But within weeks of that spill, about one-half of the oil inexplicably went missing.

“What we’re trying to figure out is: Where is all the oil at? There’s still a lot of oil that’s unaccounted for,” said Coast Guard Adm. Thad Allen, who oversaw the federal response to a catastrophe that President Obama called the “worst environmental disaster America has ever faced.” One day, oil skimmers had been scooping out of the water 25,000 barrels of oil. Then the next, they were only snaring 200 barrels. What was going on?

The drama spawned a scientific debate. Some researchers thought the oil had moved somewhere else. Others thought it had dissipated. Others pleaded for more time — they would find the missing oil. According to Nature, a sense of “panicked mania” settled over researchers. “We would love to find it to do more research on” the oil plume, said Terry Hazen of the Lawrence Berkeley National Laboratory. “But it’s not there.”

A pair of recent studies, however, point to the possibility the oil was there all along — it was just hiding. According to papers published in the Proceedings of the National Academy of Sciences and Environmental Science & Technology, while everyone was frenetically searching the waters for oil, millions of gallons of it quietly sank to the ocean floor. But it’s not exactly clear how much; estimates vary wildly in the studies.

One study, conducted by researchers at the University of California at Santa Barbara, said anywhere from 2 to 16 percent of the Deepwater Horizon oil believed to be in the deep ocean is actually on the ocean floor. Then another study published last week said somewhere between 3 and 5 percent of the oil is on the ocean floor.

“Our number is a little bit more conservative than theirs,” lead scientist Jeff Chanton, an oceanographer at Florida State University, told Live Science. But “if the two approaches agree with a factor or two, that’s pretty good for estimating all of the oil on the seafloor.”

The discovery isn’t cause for celebration, however.

For one, there’s still a lot of oil missing. “This analysis provides us with, for the first time, some closure on the question, ‘Where did the oil go and how did it get there?'” Don Rice of the National Science Foundation said in a statement. “It also alerts us that this knowledge remains largely provisional until we can fully account for the remaining” oil.

Then there’s this possibility: Though the oil has apparently separated from the water itself, it’s now burrowed so deep that it will take substantially longer to decompose. “There’s less oxygen down there,” Chanton told Live Science. “It might be there for a long period of time, a little reservoir of contamination.” He added in a statement: “Fish will likely ingest contaminants because worms ingest the sediment, and fish eat the worms. It’s a conduit for contamination into the food web.”

In 2013, Chanton developed a hypothesis that the influx of oil created what he called an underwater “dirty blizzard.” The oil mixed with deep water sediments, creating “a dirty bathtub effect.” Those sullied particles were then substantially heavier, and “fell to the ocean floor at a rate 10 times the normal deposition rates,” Chanton explained in 2013. “It was, in essence, an underwater blizzard.”

But even if he thought he had figured out how the oil sank to the bottom of the gulf, he still had to prove it. He had to find the missing oil.

That’s when he developed a novel process to search for the oil using carbon 14 — found in regular ocean sediment, but not oil. Using what’s described as an “inverse tracer,” he and other FSU researchers scanned more than 9,200 square miles near Deepwater Horizon and found that more than 3,200 square miles were stained with oil, reported Live Science.

The FSU research was funded with money set aside by BP for studying the effect of the Deepwater Horizon spill on the gulf. But BP has now raised questions about the work, calling the study’s methodology “flawed,” according to a statement reported by Salon. BP has waged a great many court battles and contested many findings about the spill. Most recently, it disputed the government’s estimate that 4.2 million barrels gushed into the ocean. It said the number was really 2.4 million. This month, a federal judge in Louisiana split the difference, saying Deepwater Horizon leaked 3.2 million barrels.

Scientists, however, remain convinced that the oil is down there. “Some combination of chemistry, biology and physics ultimately caused those droplets to rain down another 1,000 feet to rest on the sea floor,” David Valentine of the University of California at Santa Barbara said in a statement.