New Zealand Oil & Gas says reserves at the Kupe field are likely to be increased for the first time since 2010 after the latest assessment by the operator, Origin Energy.
"This preliminary information suggests that the estimate of remaining Kupe reserves may need to be further increased," the Wellington-based company said in a statement on Wednesday.
Details of the assessment are confidential until the Kupe partners meet to agree on the interpretation, which is scheduled for mid-July.
Kupe lies 30km off the south Taranaki coast. Its output is processed at a station near Hawera that has been producing natural gas, LPG and light oil since December 2009.
The initial proved and probable reserves were revised upward in July 2010 to 273 petajoules of gas, 1,114 kilotonnes of LPG and 18.6 million barrels of light oil.
NZ Oil & Gas owns 15 per cent of the field. Origin holds 50 percent, Genesis Energy 31 per cent and Mitsui E&P Australia Pty holds 4 per cent.
NZ Oil & Gas decided to flag the likely upgrade to meet its continuous disclosure obligations, spokesman Chris Roberts said.
While the assessment was preliminary and confidential "the indications are significant enough we had to at least give the market a head's up," he said.
Shares of the company rose 1.9 per cent to 79 cents on the NZX on Wednesday morning and have gained about 12 per cent in the past six months.
NZN