I wouldn't fret over this too much. I don't know if it will happen or not. My guess it doesn't.
CNOOC is offering $67 in cash. Chevron is offering $65 in cash and stock. I believe Unocal's board has already accepted Chevron's offer. CNOOC had been involved in the initial bidding but lost. This was a late offer.
CNOOC is controlled by the Chinese government. A strong argument can be made that if our own government isn't going to buy our own oil assets, then why would we let a foreign government? There's also a lot of China-bashing noise coming from Congress because of the currency peg and China's entry into the WTO, which has eliminated tariffs on Chinese textiles. This issue plays into the China bashing. CNOOC is negotiating with the US government to allow them to buy Unocal then sell the US oil fields to another company. That would let CNOOC keep the Asian assets, which accounts for 40% of Unocal's asset base.
Its interesting to see who has come out in favour of it. The CEO of Exxon has said the US government shouldn't block such a takeover because Americans invest a great deal abroad and such a move could mean American firms will be blocked out of foreign fields. Also, the workers have come out in favour of CNOOC because CNOOC has said it won't lay off a single worker while Chevron will.