PetroChina Company Limited, a subsidiary of China's largest oil producer China National Petroleum Corporation (CNPC), on Wednesday announced plans for a public offering of up to 4 billion A shares on the Shanghai Stock Exchange.

A PetroChina statement said the Hong Kong-listed company had embarked on a road back to the mainland stock market, which would widen its financing sources, and strengthen its competence and profitability.

The proposal put forward by the board would be discussed at the extraordinary general meeting for shareholders on August 10. On approval, an application would be submitted to the China Securities Regulatory Commission (CSRC) and other authorities.

The issuance will raise the company's total stock to more than 183 billion shares, up by 2.18 percent, and reduce the ratio of H shares traded in Hong Kong and the United States from 11.79 to 11.53 percent.

"Investors who purchase the yuan-denominated A shares will be treated exactly the same as existing mainland shareholders and those in Hong Kong, " said the statement. "Profits available for distribution before the issuance will also be shared in by all investors according to their shareholding."

The statement said the fund would be mainly used to finance the exploration and development of domestic petroleum and gas resources, the construction of large refinery, petrochemical and gas pipeline projects, and the acquisition of overseas petroleum and gas resources.

The price of the offering is yet to be decided.

Wang Jing, a researcher with the Orient Securities Company Limited, predicted the A shares would be more expensive than H shares because a premium exists on mainland stock markets.

The H shares of PetroChina are listed on the main board of the Hong Kong Stock Exchange and on the New York Stock Exchange.

Trading of A shares is limited to mainland investors and a handful of foreign institutions.

China's securities regulators have been encouraging blue-chip Chinese firms listed overseas to return to the A share market to stabilize the mainland bourses.

Hong Kong-listed China National Offshore Oil Company Limited (CNOOC Ltd.), the listed unit of China National Offshore Oil Corporation (CNOOC), China's largest offshore oil company and third largest oil producer, is another big company expected to list on the A share market.

PetroChina's share price closed Wednesday at 11.74 HK dollars, up more than 5 percent from the closing price 11.16 HK dollars on the previous trading day on Monday.