Experts are also warning that majority of the oil is trapped under Gulf beaches and could remain there for years.
A National Oceanic and Atmospheric Administration (NOAA) report has claimed 33 percent oil has been burned, skimmed, dispersed, or directly recovered by cleanup operations.
Another 25 percent has evaporated into the atmosphere or dissolved in the ocean, and 16 percent has been dispersed via natural break-up of the oil into microscopic droplets.
The remaining 26 percent, the report says, is still either on or just below the surface, has washed ashore or been collected from shores, or is buried along the coasts.
But scientists argue that fluid nature of the ocean means that it's "exceedingly hard" to track oil.
According to National Geographic News, to University of South Florida chemical oceanographer David Hollander, the NOAA estimates are "ludicrous."
"It's almost comical," he said.
Hollander said that while 25 percent can be accounted for (by burning, skimming etc), 75 percent is still unaccounted for.
For instance, the report considers all submerged oil to be dispersed and therefore not harmful, but that's not the case.
This week, biological oceanographer Markus Huettel and colleague Joel Kostka dug trenches on a cleaned Pensacola beach and discovered large swaths of oil up to two feet deep.
And 'oil-breaking' by microbes depends on how much oxygen is available for the tiny organisms.
Microbes are not an oil-cleanup panacea either, cautioned LSU's Carney.
"The sentimentality that bacteria turn everything into fish food and CO2 is total bull," he said.
Plus, they selectively break oil, and take ages to do it.
Then remains the question of oil in deep oceans. The mixture of oil and chemical dispersants may be suspended and preserved, causing long-term problems for deep-sea animals, said Texas Tech University ecotoxicologist Ron Kendall.
"We're getting into something different than the 2-D petroleum spill" on the Gulf's surface, said Hollander.
"All of the sudden you've taken this 2-D disaster and turned it into a 3-D catastrophe," he added. (ANI)