This summer, the state-owned China National Offshore Oil Corp. (CNOOC) announced that it was bidding $15.1 billion to acquire Canadian oil company Nexen Inc. If approved, the deal would be the largest overseas acquisition by a Chinese company.

This isn’t the first time that CNOOC has tried to buy a North American energy producer, however. In 2005 CNOOC bid $18.5 billion to take over American oil company Unocal Corporation. That deal was blocked by U.S. politicians who contended, among other things, that it posed a threat to national security. CNOOC ultimately withdrew its bid.