China National Offshore Oil Corp. reportedly may bid nearly $20 billion in cash for Unocal Corp. sometime this week, trumping Chevron Corp.’s $16 billion stock-and-cash offer made on April 4.

China’s state-run energy firm would offer about $71.50 a share, an 8 percent premium over Unocal’s closing share price yesterday, Bloomberg News reported.

But with a board meeting scheduled this week, it’s still not clear whether directors of the third-largest Chinese oil and gas producer will support a bid, Reuters said Tuesday.

CNOOC decided to move quickly on its bid for Unocal because the Securities and Exchange Commission is poised to approve the disclosure documents on Chevron’s bid. The Federal Trade Commission approved Chevron’s takeover plan on June 10.

On Monday, two U.S. congressmen asked the Bush administration to review and potentially block any effort by CNOOC Ltd. to acquire Unocal, The Wall Street Journal reported. Richard Pombo and Duncan Hunter, Republican congressmen from California, urged President Bush to exercise his authority under a 1988 federal law to begin a review by the Committee on Foreign Investments in the U.S.

If the deal goes through, it would be the biggest ever overseas acquisition by a Chinese firm. Both Chevron and CNOOC are interested in Unocal for its vast oil and gas assets in Asia.

The news Tuesday helped drive Unocal shares up 2.2 percent to settle at $64.85.