When the British Petroleum oil rig Deepwater Horizon was forced to shut down temporarily because of a gas surge, one engineer tried to persuade his colleagues that a liner was required to secure the pipe. The proposal, which would have cost about $7 million, was rejected by management. “This has been a nightmare well which has everyone all over the place,” the engineer wrote to a colleague. Six days later, on April 20, 2010, the rig exploded in the Gulf of Mexico and spilled more than four million barrels of oil before it was capped almost three months later.