When an offshore oil rig is outdated, or can no longer cost-effectively pump oil, most countries require that the oil rigs be wholly decommissioned.

FORBES: Environmental Scientists Urge That Decommissioned Oil Rigs Be Transformed Into Artificial Reefs

Private equity backed 2Co wants to build a new coal plant above the Hatfield coal mine and pump the gas to North Sea oil fields where it can be used for enhanced oil recovery.

BBC: Carbon dioxide from industry could be buried offshore

Too many wells release the natural pressure in the field, like fizz from a soda can, and it becomes too expensive to pump the oil out.

FORBES: The YouTube Solution

One danger is that, as the oil slowly oozes out, it might leak into the ground water before a drilling rig can pump it out.

NPR: Industry Seeks to Extract Oil from Rocky Mountain Shale