#5. Piper Alpha Oil Rig $3.4 Billion

The world's worst off-shore oil disaster. At one time, it was the world's single largest oil producer, spewing out 317,000 barrels of oil per day. On July 6, 1988, as part of routine maintenance, technicians removed and checked safety valves which were essential in preventing dangerous build-up of liquid gas. There were 100 identical safety valves which were checked. Unfortunately, the technicians made a mistake and forgot to replace one of them. At 10 PM that same night, a technician pressed a start button for the liquid gas pumps and the world's most expensive oil rig accident was set in motion.
Within 2 hours, the 300 foot platform was engulfed in flames. It eventually collapsed, killing 167 workers and resulting in $3.4 Billion in damages.

#3. Prestige Oil Spill $12 Billion

On November 13, 2002, the Prestige oil tanker was carrying 77,000 tons of heavy fuel oil when one of its twelve tanks burst during a storm off Galicia, Spain. Fearing that the ship would sink, the captain called for help from Spanish rescue workers, expecting them to take the ship into harbour. However, pressure from local authorities forced the captain to steer the ship away from the coast. The captain tried to get help from the French and Portuguese authorities, but they too ordered the ship away from their shores. The storm eventually took its toll on the ship resulting in the tanker splitting in half and releasing 20 million gallons oil into the sea.
According to a report by the Pontevedra Economist Board, the total cleanup cost $12 billion.

#1. Chernobyl $200 Billion

On April 26, 1986, the world witnessed the costliest accident in history. The Chernobyl disaster has been called the biggest socio-economic catastrophe in peacetime history. 50% of the area of Ukraine is in some way contaminated. Over 200,000 people had to be evacuated and resettled while 1.7 million people were directly affected by the disaster. The death toll attributed to Chernobyl, including people who died from cancer years later, is estimated at 125,000. The total costs including cleanup, resettlement, and compensation to victims has been estimated to be roughly $200 Billion. The cost of a new steel shelter for the Chernobyl nuclear plant will cost $2 billion alone. The accident was officially attributed to power plant operators who violated plant procedures and were ignorant of the safety requirements needed.