TORONTO - CNOOC Ltd, China's largest offshore oil and gas producer, fulfilled one of the terms made for its $15.1 billion acquisition of Calgary-based oil and gas producer Nexen Inc as it made its trading debut on Canada's largest stock market Wednesday morning.

The State-owned oil company, now listed under the symbol CNU on the Toronto Stock Exchange (TSX), has been approved to trade American Depositary Receipts (ADRs), which is equivalent to 100 common shares of CNOOC Ltd.

No new shares will be issued and it won't generate additional funds for the company. Instead, CNOOC's chairman Wang Yilin and CEO Li Fanrong -- who were both in Toronto to debut their listing - - said this not only represents their commitment to maintaining transparency and good corporate governance in the countries where they operate, but also gives investors more options.

"This further embodies the company's philosophy of proper management of operations in countries where it runs business or invests in," said Li. "It also provides investors with more choices in terms of exchange venues and currencies."

Pursuing a listing in Toronto is just one of many commitments CNOOC made to win the Canadian government's approval for the Nexen deal, one that is considered the biggest ever overseas corporate takeover by a Chinese company. CNOOC also pledged to retain Nexen' s 3,000 employees and make Calgary the headquarters of its North American operations.

So far, Li said things have been on track since they closed the deal in February.

"The integration process has been pushing forward steadily in the past seven months since we bought Nexen in February as we were expected," said Li, adding "The Beijing headquarter has been in extensive touch with its Calgary office and Nexen company."

Posting a 7.9-percent gain for the first half of the year, things are looking up for CNOOC. But Li stressed that there are still some challenges ahead.

"As an oil and gas producer, the most difficult challenge in the integration process is how we could find high quality assets consistently and make the best of them to bring more benefits to our company and shareholders," he said.

CNOOC Ltd is also listed in Hong Kong and on the New York Stock Exchange.