Union Oil Company of California, and its holding company Unocal Corporation, together known as Unocal was a major petroleum explorer and marketer in the late 19th century, through the 20th century, and into the early 21st century. It was headquartered in El Segundo, California, United States.

Unocal was involved in domestic and global energy projects. Unocal was one of the key players in the CentGas