UPDATE 2-Qatar Petroleum unit IPO heavily oversubscribed

(Adds value of company, number of shares on offer)

By Ola Galal

DUBAI, March 23 (Reuters) - Investors offered 8.9 billion riyals ($2.45 billion) for shares of a new Qatar Petroleum unit that runs three of its service businesses, five times more than the state firm was seeking in the initial public offering.

Gulf International Services, which owns some Qatar Petroleum transport, insurance and drilling services operations, offered stock at 21 riyals per share, plus a 0.6-riyal offering cost, it said in a statement received late on Saturday.

The 80.844 million shares represent a 65.8 percent stake valuing the company at $710 million.

Qatar Petroleum is the state energy firm of Qatar, the world's largest exporter of liquefied natural gas and an OPEC oil producer.

It set up Gulf International Services as a holding company to control three subsidiaries -- Gulf Helicopter Co, Gulf Drilling Co and Al-Koot Insurance and Reinsurance Co.

Qatar Petroleum said last month it would look to sell a further 4.2 percent of Gulf International to "selected institutions" and keep 30 percent of the company.

HSBC Holdings Plc advised on the IPO.