"It was surprising how fast they consumed the oil. In some locations, it took only one day for them to reduce a gallon of oil to a half-gallon. In others, the half-life for a given quantity of spilled oil was six days."
"It's a little bit surprising to some people that the Gulf is so clean given all of that oil that's going into the Gulf, and the other toxic chemicals from the Mississippi River."
"Petroleum degraders are found anywhere ... And that's logical because it (oil) is a natural product. Basically it's fossilized algae that have been compressed under extreme heat."
Terry Hazen, biologist, University of Tennessee

Scientific studies distilled from research after the 2010  Deepwater Horizon oil spill seems to conclude that nature' trumps human intervention always and forever. Airplanes that sprayed chemicals for the purpose of breaking up oil slicks succeeded in poisoning sea creatures, and caused the oil to remain longer than it would have had no intervention occurred.

Naturally-occurring bacteria may have mitigated much of the damage 

The Gulf and its environs have, under the biological influence of nature, self-cleaned to an amazing degree. Nature's microbes swiftly took over when the oil spill occurred. That seems to make sense to scientists who are aware that oil deposits existing beneath the ocean bottom release up to 1.4 million barrels of oil into the Gulf annually -- according to the U.S. National Research Council.

And nature's formula for balance sends out oil-dispatching bacteria in response. In deep water, bacteria are drawn to oil "like little oil-seeking missiles", in the words of Professor Hazen.

Oceans manage, with nature's benevolent guidance, to clean up oil spills in a manner exceedingly superior to what humans can devise. Fisheries and beaches contaminated when the tanker Amoco Cadiz split on Northern France's coastline in 1978 treated with chemicals took fifteen to twenty years to recover. Those areas that weren't treated recovered within five years.

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