<human>:  When did the Exxon Valdez oil spill happen?
<bot>: The Exxon Valdez oil spill happened in 1989. It was caused by an oil tanker called the Exxon Valdez, which was owned by Exxon Shipping Company. The ship was transporting oil from Alaska to the West Coast of the United States when it ran aground on Bligh Reef in Prince William Sound, Alaska.