India's Gujarat State Petroleum Corporation (GSPC) has made the country's biggest natural gas discovery.
India currently imports more than half its gas supplies
GSPC has discovered 20 trillion cubic feet of gas, worth £27bn ($50bn), four miles off the Andhra Pradesh coast in the southeast of the country.
India's biggest previous gas find of 14 trillion cubic feet was in the same Krishna Godavari basin area.
India also hopes to start importing gas from Iran, despite US opposition.
The announcement of GSPC's find was made by Narendra Modi, the chief minister of the Gujarat state government, which owns 95% of the company.
Big energy consumer
Over the past six years GSPC has grown from operating small fields in Gujarat in northwest Indian, into a major national oil and gas explorer and producer with 21 oil and gas sites.
India is one of the world's largest energy consumers, and its gas and oil consumption is expected to grow still further as its economy grows.
It currently produces under half the gas it needs.
The US opposes India's plans to import gas from Iran - via a pipeline through Pakistan - because of Washington's opposition to the Iranian regime and Iran's nuclear programme.