PetroChina, the biggest oil producer in Asia, has moved closer to selling HK$50 billion worth of shares in Shanghai as the China Securities Regulatory Commission said yesterday it would review the share sale on Monday. The CSRC announcement comes after United States billionaire William Buffett trimmed the PetroChina stake held by his firm for the third time in two months. Mr Buffett's hedge fund Berkshire Hathaway raised US$41 million from selling 28 million shares at an average price of HK$11.47 each on September 6, according to stock exchange filings. The sale reduced his stake to 8.93 per cent from 9.07 per cent. PetroChina will sell as many as four billion shares for an A-share listing in Shanghai to fund expansion. Its Hong Kong-listed shares rose 3.51 per cent to HK$12.38 yesterday. PetroChina won shareholders' approval for the offering last month. Chairman Jiang Jiemin said at the time the oil giant wanted to price its A shares at a discount to its Hong Kong-listed shares. Mainland firms tend to price their A-share offerings lower than their H shares, a practice that has led to substantial gains in trading debuts because investors place higher values on stocks listed in the mainland. Shares in the mainland trade at an average 53 times earnings compared to 17 in Hong Kong. Bank of Communications surged 71 per cent on its mainland debut after pricing its A shares 4.8 per cent lower than its H shares in late April. Ping An Insurance's shares in February jumped 38 per cent on their mainland debut after the shares were priced at an 11.3 per cent discount, while China Life Insurance's shares soared 106 per cent after being priced at a 22.3 per cent discount. The CSRC has been criticised for underpricing initial public offerings, over which it has pricing authority. Critics said the action encouraged speculation and undercut government revenue from share sales. Analysts said Beijing was eager to see quality firms issue shares at low prices to siphon off funds from speculative shares to deflate a market bubble. PetroChina plans to spend 40 billion yuan developing the Jidong Nanpu field, the country's biggest discovery in almost 50 years. The company said in March that spending could rise as much as 24 per cent to US$24.5 billion this year. PetroChina signed a A$45 billion (HK$302 billion) deal last year to take liquefied natural gas from Australia's Woodside Petroleum for up to 20 years.