In a Bloomberg article this morning, Chinese investors got their first chance to own PetroChina (NYSE: PTR)'s Class-A shares, as the shares began trading in their Shanghai debut today. As the trading day ended in Shanghai, Chinese investors bid up the Beijing-based state-owned oil company to value the firm at $1.1 trillion, more than Exxon Mobil (NYSE: XOM) and General Electric (NYSE: GE) combined.

The stock is now so big that Bloomberg reports, "The rally makes PetroChina shares four times more expensive relative to earnings than those of Exxon, whose sales are almost four times higher. China's entire stock market was valued at less than $1.1 trillion before tripling this year and giving the communist nation five of the world's 10 biggest companies."

BloggingStocks' own Michael Fowlkes had a post last week portending to Exxon's fall from the perch of world's largest company. A-shares, which PetroChina listed today, are traded in Shanghai and Shenzhen stock exchanges and are open to domestic investors and qualified foreign institutional investors. Their popularity has soared recently as China has made provisions to allow more open investing in the A-share market to strategic overseas investors.

Other Chinese companies that rank among the world's 10 largest by market value are China Petroleum, known as Sinopec (NYSE: SNP), China Mobile Ltd. (NYSE: CHL), Industrial & Commercial Bank of China Ltd. and China Construction Bank Corp. (OTC: CICHF).

While everyone seems to think China is going to the moon, billionaire uber-investor Warren Buffet has cautioned investors looking to make money in Chinese markets. In fact, Buffett's Berkshire Hathaway (NYSE: BRK.A) sold its stake in PetroChina this year, reaping an eightfold gain that contributed to a 64% increase in third-quarter profit for the Omaha-based company. Berkshire had 2.34 billion shares as of the end of 2006, the largest holding after state-owned China National Petroleum Corp.

DISCLOSURE: I have clients who own BRK.A and exchange-traded Chinese fund, FXI.

Zack Miller is the lead equity analyst for America Israel Investment Associates, LLC., the managing editor of IsraelNewsletter.com and a former equity analyst for a leading multinational hedge fund.