Dispersant's sprayed on it would be the answer. The idea is that the dispersant's basically just made the oil sink; out of sight, out of mind.
I do not that this is for sure the case; but that has been widely speculated.
Dispersant's destroy surface tension and break the oil up into smaller droplets, allowing the sun, oxygen, and oil eating microcritters to break it down faster.
Be careful my friend, you are very close to following the environmental Pied Piper's tune dancing right over the edge. Not all the way, but CLOSE.
The dispersants "disperse" the oil into the water, increasing it's surface area by millions so the oleophilic bacteria can go after the oil (a process that has happened since BEFORE man walked on the pristine beaches!).
The whole story is at The Patriot's Flag - Dispersants and the Piper where I laid out the technology for anyone to be able to follow.
And I was RIGHT ... and I'm muttering "I told you so" under my breath. All the dispersants do is "nudge" Mother Nature into doing HER job better ... but SHE HAS ALWAYS DONE THE JOB ... oil leaks into the worlds oceans every day ... and the reason we still have beaches are the oleophilics.
That dispersant in the oil causing it to sink has to be as big a scam as global warming! Show me one instant in the oil spewing videos where the dispersant is sinking on its own? Nowhere. Dispersant BS story to the max.
Dispersants can act like a surfactant and break up large clumps of oil into smaller droplets. It would still float though.
By the time it settles on the bottom, tar balls are the result. They also occur down here naturally... but not to this extent. The marshes are where the damage is... they never talk about that or show the wildlife covered in this tar substance.
LLS