Hong Kong-listed PetroChina Co Ltd, the country's largest oil and gas producer, has appointed three securities companies as its mainland IPO underwriters, said sources.

The three securities companies are UBS Securities, the Swiss bank's joint venture with Beijing Securities; China International Capital Corp Ltd; and China CITIC Securities.

Earlier this month, PetroChina filed its application with mainland regulators to sell up to 4 billion A-shares through an initial public offering in Shanghai.