It is understood the Independent Expert, Netherland Sewell and Associates International, is named as main party to the proceedings, with the government, Maui partners Shell NZ, Todd Energy and OMV, together with Contact Energy and NGC as other defendants.

EnergyReview.Net on Monday said such a challenge was likely over the methodology used by NSAI to reach its conclusions. Methanex, this country's largest gas user, said it and its advisors were currently studying the report and considering the various courses of action open with respect to the redetermination process.