Greymouth had already purchased, in late 2007, the other 20% stake in the Kowhai exploration licence PEP 38742 from Ballance Agri-Nutrients' subsidiary Petrochem Ltd.
"The acquisition of the Swift interest in the Kowhai discovery is a valuable addition to Greymouth's gas and condensate properties in north Taranaki," Greymouth chief executive Mark Dunphy said.
PEP 38742 is next to Greymouth's commercial Turangi field and close to several other Greymouth permits.
Swift had drilled two wells in PEP 38742 - the 2005 shallow Karaka-A1, which targeted Miocene-aged sands, and Kowhai-A1 in 2006, which targeted several Eocene-aged formations. Swift deemed neither to be commercial.
Last December, Origin Energy and its New Zealand subsidiary Contact Energy said they would pay about $US87.8 million for the majority of Swift's New Zealand assets. The deal is expected to be finalised before the end of this month.
According to Crown Minerals, PEP 38742 was the sole remaining New Zealand licence Swift had to sell.