A major Chinese oil company, CNOOC, has given up an $18.5 billion bid to take over the U.S.-based Unocal oil company.

It would have been the largest-ever Chinese acquisition of a U.S. company.

With oil prices at record-high levels, the bid sparked opposition from members of the U.S. Congress. Some politicians said losing control of some U.S.-owned oil assets could harm the nation's economy and security.

The parent company of CNOOC is controlled by the Chinese government.

A statement on the company web site said its interests are "purely commercial" and called the political opposition "unjustified" and harmful to Unocal shareholders and employees.

Ending CNOOC's bid leaves Chevron as the only bidder for Unocal.