Gulf gusher is far and away the biggest U.S. spill
As cleanup efforts progress, scientists try to track oil roaming below the surface
The catastrophic explosion on April 20 of an offshore oil-exploration platform in the Gulf of Mexico sent oil slicks coasting toward shorelines from Louisiana to Florida. Now research vessels are tracking a more stealthy threat: huge clouds of diffuse, nearly invisible oil droplets hovering deep below the surface.
