China's CNOOC Ltd. (search) (CEO) on Monday reiterated a commitment to not only retain the jobs of "substantially" all of Unocal Corp.'s (UCL) staff, but also keep its U.S. oil and gas production output in the United States, a letter to members of U.S. Congress said.

CNOOC offered $18.5 billion in cash last week to acquire the U.S.-based Unocal, a richer bid than the $16-billion plus cash and stock offer the company already accepted from Chevron (CVX). Chevron is pushing for an August vote on that offer.

The CNOOC letter came in response to a letter from more than 40 U.S. lawmakers urging the Bush administration to take a closer look at the bid.

"We had planned for and want to participate in a (government) review of the transaction as soon as possible," CNOOC Chairman and Chief Executive Officer Fu Chengyu said in a statement. "We believe it is vital to the success of the possible merged company."

Executives from CNOOC are headed to the United States this week to discuss the bid with Unocal, a person familiar with the matter told Reuters on Monday.

CNOOC has said all along it welcomed a review by the Committee on Foreign Investment (search) in the United States, or CFIUS, a body chaired by the secretary of the Treasury that reviews acquisitions of U.S. companies by foreign concerns where there could be national-security implications.

CNOOC shares were up 1.5 percent at $55.72 in midday trading on the New York Stock Exchange, while Unocal was up 23 cents at $65.91 and Chevron was up 1.1 percent at $57.33.