On June 3, 1979, workers aboard the Sedco 135-F semisubmersible drilling rig located in Mexico's Bay of Campeche removed pipe from the Ixtoc-1 well to change the drill-bit.
During this routine process, oil and natural gas under tremendous geologic pressure overcame the weight of the drilling mud and the well blew out. The blowout preventer--a device designed to close the well in the event of a just such an emergency--activated but wasn't powerful enough to shear through the thick pipe being pulled out of the well.
The result was devastating. Hydrocarbons gushing from the well ignited at the surface, and the 63 rig workers, some injured and burned, were rescued before the rig sank. Gas bubbling from the well continued to burn on the surface long after the rig went down.
For some perspective, the Pemex spill took 290 days to stop, and it was only at 160 feet, not 5000+ feet.