Early evening photos of Nexen"s Galaxy III offshore rigs with the newly installed fourth platform in the foreground in the North Sea is pictured in this May 2010 aerial view handout photo. Reuters

State-owned CNOOC Ltd launched China's richest foreign takeover bid yet on Monday by agreeing to buy Canadian oil producer Nexen Inc for US$15.1 billion.

CNOOC, China's third-largest oil company, hopes to sell the deal to shareholders and the government with a hefty 61 percent premium to Nexen's Friday stock price. It promised to retain all employees and to make Canada home base for its Western Hemisphere operations.

CNOOC is offering $27.50 cash a share for Nexen, which has oil sands operations in the Canadian province of Alberta, shale gas in the province of British Columbia and extensive exploration and production holdings in the North Sea, Gulf of Mexico and offshore West Africa.

The initial shareholder reaction was enthusiastic. Shares of Nexen, whose board unanimously approved the deal, surged C$9.06, or 52 percent, to C$26.35 in Toronto on Monday.

The move is the most ambitious foray by China into North American energy since a 2005 attempt to buy U.S.-based Unocal for $18.5 billion was thwarted.

Chinese companies have been among the most aggressive in targeting assets around the globe to help feed demand in the world's second-biggest economy.

As for Canada, Prime Minister Stephen Harper has pushed to attract more energy investments from China. The CNOOC deal shows his efforts are bearing fruit, and Canada has more reasons to accept the deal than to veto it.

(Agencies)