Here's something I learned about this week: The Deepwater Horizon wellhead blowout isn't unprecedented, nor is it the largest (yet).
Ixtoc I oil spill - Wikipedia, the free encyclopedia
A Mexican-operated rig in the Gulf of Mexico, the Ixtoc I, blew out its wellhead in 1979, and was not capped until ten months later. It spilled 10000-30000 bbl/day, making it the biggest accidental oil spill ever.