State-owned exploration firm Oil and Natural Gas Corporation has struck huge oil and gas reserves west of its gigantic Bassein gas field.

"The two well drilling campaign west of Bassein gas field (off the Mumbai coast) showed presence of several hydrocarbon bearing zones that are estimated to hold around 48 million tonnes of oil and oil equivalent gas," informed sources said in New Delhi.

However, the reserves are yet to be tested and a formal announcement was likely only next month, they said.

The latest discovery, which comes close on the heals of the discovery of 97 million tonnes of oil and oil equivalent gas in East Bassein, would supplement the decline in Bassein output expected from next year.

Bassein field, which currently produces 32 million standard cubic metres per day of gas, would hit the decline stage from next year with its production falling by as much as 3 mmscmd, sources said adding ONGC would put to production its find in eastern side of the gigantic field by 2004.