The Rumaila oil field is a giant oil field located in southern Iraq, approximately 20 mi from the Kuwaiti border. The dispute between Iraq and Kuwait over allegedly slant-drilling in the field was one of reasons for Iraq's invasion of Kuwait in 1990. This field was discovered by British Petroleum (BP) in 1953. Under Saddam Hussein, it was nationalized by Iraq. Since then, this massive oil field remains under Iraqi control. Rumaila is considered the fourth largest field in the world. The field is estimated to contain some 15% of Iraq's oil reserves.