The Persian Gulf is an extension of the Indian Ocean in the Middle East. Located between Iran and the Arabian Peninsula, the Gulf has been the center of several conflicts. During the Iraq-Iran War, from 1980 to 1988, oil tankers stationed in the the Gulf were frequently targeted. During the Gulf War in 1991, the Persian Gulf was used as a launching point for United States forces as they pushed back the Iraqi invasion of Kuwait. The Persian Gulf has traditionally been a rich fishing ground, with many large coral reefs. The region immediately surrounding the Persian Gulf is the richest single source of crude oil in the world. Additionally, the world's largest off-shore oil field is located in the Persian Gulf. The area also has extensive reserves of natural gas and as a significant source of pearl oysters. In recent years, the ecological health of the Persian Gulf has caused some concern, mostly due to the numerous oil spills that have occurred as a result of war and industrial accidents.