Up to $60 million will be spent on looking for more oil in the Tui field.
New Zealand Oil and Gas has a 12.5% stake in the declining field, which accounted for a third of its $116 million revenue, with the rest coming from Kupe.
Chief executive Andrew Knight says it and its partners are optimistic further exploration will lengthen the life of the Tui field.
He says the investment will be significant, somewhere north of $50-$60 million in total, and the returns will be very attractive - although it's too early to talk about volumes.
Higher oil prices boosted the energy explorer's full-year profit to $19.9 million, a turnaround from last year's $75.9 million loss, when it wrote down its investment in the Pike River coalmine.
Apart from taking early steps into Tunisia and Indonesia to boost earnings, Mr Knight says NZOG is now considering once again exploring onshore Taranaki.
He says some other parties have an advantage over NZOG in onshore New Zealand because of decisions the company has made in the past, when it decided not to go onshore.
Mr Knight says that because a lot of the onshore acreage has been taken up, it's now looking at the blocks offer, an annual tender process for the allocation of oil and gas exploration permits, introduced by the Government this year.