Both ONGC and IOC bought shares in each other in 1999 under instructions from the government, which wanted to ensure it got enough money from the sale of state-owned businesses.
Mr Raha also said ONGC will start purchasing an additional 80,000 metric tonne of crude oil from Nigeria in two months. "We expect to sign the final agreement in two months to enable us to lift the additional oil that Nigeria has offered," he said.
ONGC currently buys 40,000 tonne of oil from Nigeria. The offer came after ONGC Mittal Energy Ltd signed an agreement on November 10 to invest as much as $6 billion in oil refining and power in Nigeria in exchange for drilling rights.
The investment will depend on the oil and gas yields from exploration areas to be allotted by Nigeria.
ONGC has also advanced its target date for acquiring overseas oil and gas assets yielding as much as 20 million tonne of oil and gas equivalent to 2010 from 2020.
"Acquisitions are being speeded up to bridge a supply gap that is widening because of stagnating local oil and gas production and rising demand," the oil ministry said in a statement issued today at an annual Economic Editors' Conference in New Delhi.