When the Deepwater Horizon offshore oil rig in the Gulf of Mexico exploded on April 20, 2010, it set off an oil spill that may exceed the extent and impact of the 1989 Exxon Valdez spill in Alaska's Prince William Sound. Of grave concern is the oil's near- and long-term effects on both wildlife species and Gulf ecosystems at large. In this Bio Bulletin, view satellite imagery of the shifting surface oil and learn what's at stake.