Officials warn the $200 million set aside to encourage gas exploration may be too small - with production falling and closure of the ageing Māui field looming.

The Government's widening the scope and terms of the commercial co-investment fund.

BusinessDesk reports a Cabinet paper released today states the field will stop production, with the rest of the sentence redacted.

Resources Minister Shane Jones says he isn't privy to when the closure will happen.

"We're suffering a decline in the known reserves from those historically large sites and they're working through the process - it's up to them to identify when it will actually cease."

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