In late July, 2010, tropical storm Bonnie passed through the Gulf of Mexico. It wasn't clear what it would do to the oil leaked into the water there. NASA has been heavily monitoring the oil using satellites, and on July 28 took this image with the Aqua satellite:
[Click to enlarge.] The swirls are likely to be oil still floating in the water. It's not completely certain because there are other factors that can affect this type of imagery. However, it does appear that Bonnie dissipated some of the surface slick, though the oil remaining is apparently not recoverable.
NASA imagery like this can help efforts to clean up the leak, as well as understand how disasters like this propagate. And don't forget: this only shows the surface oil. Hundreds of millions of liters of oil roared up from beneath the Earth's surface. It may be decades before we learn the full extent of the damage wrought.
NASA has also provided a fascinating FAQ about their satellite imagery of the region. I suggest reading it. More knowledge is a good thing.
Image credit: Jeff Schmaltz, MODIS Rapid Response Team