Production of natural gas at the Kinsale Head gas field, off the Cork coast, has ceased after 42 years.
The final commercial volumes of indigenous Irish gas flowed through the Inch terminal last week.
Kinsale Energy Limited first signalled two years ago that reserves in the fields at Old Head of Kinsale, Ballycotton, Southwest Kinsale and the Seven Heads were depleting.
Plans are being drawn up to safely decommission the site.
The gas fields were the country's only indigenous source of natural gas until 2015.
They produced almost two trillion cubic feet of natural gas and enabled the development of a national gas network.
Decommissioning and removal of two giant off-shore rigs - Kinsale Alpha & Kinsale Bravo - and the plugging of wells, will take several years to complete.
The Corrib Gas Field, off the coast of Co Mayo, is now Gas Networks Ireland's only indigenous natural gas source.
The remainder is supplied via interconnectors from Moffat in Scotland.
FROM THE ARCHIVES
Ireland's first natural gas supply goes into production at Kinsale - 1978
Reports of gas find off Kinsale - 1989