A Petrovietnam official told Reuters the contract covering blocks 10 and 11.1 in the Nam Con Son Basin was signed by Petrovietnam and a venture between Petronas Cargali Overseas Bhd, Indonesia's Pertamina, and Petrovietnam Investment and Development Co (PIDC).

He said if the search was a success, 50 per cent of profits would go to Petrovietnam, while the other 50 per cent would be split between PIDC, Petronas and Pertamina.

The official said operations would soon start in the two blocks, which are some 210 km (130 miles) southeast of the southern province of Ba Ria-Vung Tau.

"If the contractors find crude oil, the deal would last 25 years. If they find gas, it will be 30 years," the official said.

Official media said the partners would operate under the name Con Son Joint Operation Co to exploit the blocks, which have a total area of nearly 8,000 square km. The official Vietnam News daily said the deal was Petrovietnam's 44th production-sharing contract with foreign oil firms since 1988.