The contract, part of a 25-billion-rupee (555-million-dollar) investment plan by ONGC to upgrade its operations, was signed last week, chairman Subir Raha told AFP in Guwahati.

"Haliburton will be using their skills and technologies to redevelop three main oilfields in Assam and we expect to increase production by about 50 percent in the next three years," Raha said.

ONGC now produces about 1.2 million tonnes annually of crude in Assam, located in northeast India, while Oil India Ltd, another state-run exploration firm, produces about 3.6 million tonnes.

More than 10,000 people have lost their lives in a separatist campaign in the tea and oil-rich state during the past two decades.

The three oilfields, Geleki, Lakwa and Lakhmani, outlined in the contract with Haliburton have stopped yielding oil in recent years after about 40-years of successful operation, Raha said.

"We know the three oilfields still have plenty of reserves and hence the decision to utilize the services of Haliburton to rediscover and optimize production," Raha said.

Assam has over 1.3 billion tonnes of proven crude oil and 156 billion cubic meters of natural gas reserves of which about an estimated 58 percent are yet to be explored, Raha said.