China's largest oil and gas producer, is expected to launch its initial public offer in Shanghai near the end of this month, sources familiar with the offer said on Saturday.

The roadshow for investors is likely to start in the last week of October, with the shares listing in Shanghai in mid-November, the sources said.

On Sept. 24, China's stock regulator approved PetroChina's plan to issue up to 4 billion new A shares in the offer, which is expected to raise around $7-8 billion, making it one of China's five biggest domestic IPOs.

IPOs are usually launched within two weeks from approval. Since Chinese markets were closed for a week-long holiday at the start of October, PetroChina had been expected to launch its offer last week.

However, the sources said the launch had been delayed slightly because government officials and markets would be preoccupied next week with a Communist Party leadership meeting, and to allow the money market to settle down after large share offers last month triggered a major funding squeeze.