CALGARY/TORONTO, Alberta (Reuters) – At first blush, CNOOC Ltd’s (0883.HK: Quote, Profile, Research, Stock Buzz) $15.1 billion bid for Nexen Inc (NXY.TO: Quote, Profile, Research, Stock Buzz) seemed like a sign that China is ready to go on a buying spree in Canada’s oil patch.

But on a closer look that seems far from certain. If Beijing thinks Nexen will open the door to a rash of big North American energy acquisitions by its state-controlled enterprises, it may want to think again.

HONG KONG/CALGARY (Reuters) – State-controlled CNOOC Ltd launched China’s richest foreign takeover bid yet on Monday by agreeing to buy Canadian oil producer Nexen Inc for $15.1 billion, forcing Ottawa to decide whether security concerns outweigh its desire for foreign investment in its energy resources.

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.