Nov. 5 (Bloomberg) -- PetroChina Co., China's biggest oil producer, fell the most ever in U.S. trading after Bear Stearns & Co. recommended investors sell the shares because they were too expensive compared with rivals such as Exxon Mobil Corp.

PetroChina's American depositary receipts slid the most since March 2000, losing $26.21, or 10 percent, to $228.85 at 11:33 a.m. in New York Stock Exchange composite trading. In Hong Kong, the stock dropped 8.2 percent to HK$18.

``We see little fundamental reason why PetroChina should outperform other Chinese oil companies or even the China market,'' wrote Bear Stearns analyst Adam Clarke, citing record oil prices and the company's completion of the biggest share sale this year.

PetroChina, the first company to be valued at $1 trillion, is ``expensive,'' said Clarke, who lowered his rating to ``underperform.'' The company trades at 21.6 times earnings in Hong Kong, 70 percent higher than Exxon Mobil, the largest U.S. oil producer. ``We see little reason for this disparity.''

Today's decline in PetroChina's U.S. and Hong Kong-listed shares occurred even after the stock almost tripled during its first day in Shanghai trading. The company's Shanghai initial public offering boosted the company's global market capitalization to over $1 trillion.

Billionaire investor Warren Buffett, which reaped an eightfold gain after his Berkshire Hathaway Inc. sold its PetroChina stake, said last month that Chinese share prices have risen too fast.

Hong Kong's Hang Seng Index tumbled the most today since the Sept. 11, 2001, terrorist attacks after Chinese Premier Wen Jiabao said his government may delay allowing mainland investors to buy Hong Kong stocks.

China Petroleum and Chemical Corp., the nation's biggest oil refiner, fell the most in almost four years in U.S. trading, declining $16.03, or 10 percent, to $142.81. Cnooc Ltd., the nation's third-largest oil producer, slumped 7.2 percent to $192.04.

To contact the reporter on this story: Lynn Thomasson in New York at lthomasson@bloomberg.net.

Last Updated: November 5, 2007 12:06 EST