EXHIBIT 21 SUBSIDIARIES OF THE REGISTRANT PERCENTAGE OF VOTING SECURITIES OWNED BY ORGANIZED IMMEDIATE NAME OF COMPANY UNDER LAWS OF PARENT --------------- ------------- ------------- Atlantic Richfield Company (Registrant)........... Delaware Subsidiaries of Registrant in consolidated financial statements, as of December 31, 1997: ARCO Alaska, Inc................................ Delaware 100.0 ARCO Chemical Company........................... Delaware 82.3 ARCO Transportation Alaska, Inc. ............... Delaware 100.0 Vastar Resources, Inc. ......................... Delaware 82.2 The subsidiaries whose names are not listed above, if considered in the aggregate as a single subsidiary, would not constitute a significant subsidiary.