48°30′S · 172°00′E The Great South Basin Survey of a national endowment

A hundred thousand square kilometres of maybe.

South-east of Otago and Southland, beneath up to a kilometre of the world's roughest water, lies New Zealand's largest under-explored petroleum province. Nine wells in fifty years. One discovery. Estimates that run to ten times the Maui field. This page is a survey of what might be down there — and of what a disciplined country could turn it into.

~100,000 km²
basin area — close to the size of the North Island
up to 9 km
of sediment beneath the seabed
9 wells
ever drilled · 4 found hydrocarbons
NZ$0
of petroleum revenue ever saved by the Crown
begin the descent
STN 01The water column−100 m to −1,250 m

A drowned rift at the edge of Gondwana

When the ancient supercontinent tore apart about 83 million years ago, the stretching crust south-east of what is now the South Island sagged into a deep depression, and rivers, swamps and finally the sea filled it with up to nine kilometres of sediment. Buried inside are coal-rich source rocks of the same family that made Taranaki New Zealand's only producing petroleum basin — cooked, over geological time, into gas and light oil.

Bathymetry: Natural Earth 10 m · contours 200–5,000 m

Select a well on the map to read its story. Green marks the basin's one discovery; blue marks the dry holes and the near-misses.

The basin's geological extent is ~100,000–130,000 km², depending on how the boundary is drawn. The “500,000 km²” sometimes quoted was the Crown's 2007 marketing figure, inherited from the vast 1970s Hunt permit — not the geology.

Water depth
100–1,250 m
averaging ~700 m — deep, but routine for modern offshore development
Sedimentary fill
8.6–9 km
Cretaceous to recent; thickest in the Central Sub-basin
Source rock
2–75% TOC
Hoiho Group coal measures — proven to have generated the Kawau condensate
Conditions
Roaring Forties
the operating environment every explorer has cited on the way out
STN 02The drilling record1969 — 2026

Fifty years of glimpses

Every era of global exploration has taken one look at the Great South Basin. Texan wildcatters in the seventies. The supermajors in the 2000s. Each found just enough to keep the question alive — and left before answering it.

1969

Hunt Petroleum takes on 402,000 km²

Texas's Hunt International Petroleum acquires one of the largest exploration licences in the world over the southern offshore, and shoots more than 30,000 km of seismic lines over 13 years.

1976

Toroa-1: oil in the cuttings, answer lost

The first well finds more than 300 metres of oil shows — drillers described cuttings “dripping with oil” — but the bore is accidentally cemented during casing and can never be tested. The basin's most tantalising data point is still untested today.

1977

Kawau-1A: the discovery

Hunt's third well flows gas and 47.8° API condensate to surface — the basin's first and only discovery, originally estimated at 461 billion cubic feet. Sub-commercial in 1977: there was no gas market within a thousand kilometres.

The drill-stem test over 3,224–3,329 m flowed 6.7 million cubic feet of gas per day plus condensate from the Kawau Sandstone. A later remapping put P50 volumes at 217 Bcf. Under today's classification it is a contingent resource — found, measured, never developed.
1978–84

Five more wells, fading interest

Hoiho-1C, Tara-1 and Takapu-1A (1978), then Placid Oil's Pukaki-1 and Rakiura-1 (~1983–84). Gas shows in some, little in others. With oil cheap and the water rough, the permit is relinquished in April 1985.

2007

The supermajors arrive

After a Crown-funded seismic survey, five permits are awarded: ExxonMobil–Todd take one block, an OMV–PTTEP–Mitsui consortium takes three. The two main groups are expected to spend ~NZ$1.2 billion. The government's backgrounder floats a potential of “up to ten times” the Maui field — unproven, it notes.

2010

ExxonMobil walks

After three years of seismic work and a failed farm-down: “high technical risk, made worse by its remote location and harsh operating environment.”

2011–14

Shell's turn

Shell farms in and takes over operating the OMV permits, shoots the basin's first large 3D survey (~US$50m), and in January 2014 announces a ~NZ$200m well targeting a gas field “at least the size of Maui”, with a 30% chance of success.

2015

Shelved in the oil crash

Two days after abandoning Arctic exploration, Shell shelves the Great South Basin well, citing “complex geology”. Shell exits New Zealand entirely in 2018, selling its stake to OMV.

2018

The ban

The Crown Minerals (Petroleum) Amendment Act ends all new offshore exploration permits. Existing permits are grandfathered — OMV can still drill, but nobody can follow.

2020

Tawhaki-1 comes up dry

OMV, with Beach Energy and Mitsui, drills the basin's first well in 36 years — ~NZ$80m, in 1,300 m of water, testing a huge basement-drape structure. No hydrocarbons in the target reservoir. Fourteen of OMV's fifteen mapped leads remain untested.

2021

The basin goes quiet

The OMV joint venture surrenders its permit; New Zealand Oil & Gas relinquishes the last one — Toroa, held with Woodside — blaming the dry hole, rig costs, and “adverse regulatory settings”. For the first time since 1969, no one holds exploration rights anywhere in the basin.

2025

The door reopens

The Crown Minerals Amendment Act 2025 repeals the offshore ban — over public submissions running 94.5% opposed — restores the Act's purpose to “promote” extraction, and Budget 2025 sets aside NZ$200m for Crown co-investment in new gas fields. All acreage, including the Great South Basin, is open to application.

2026

Open — and untouched

Five new permit applications have been lodged nationally. Every one is in Taranaki or Waikato. Nobody has yet asked for the Great South Basin.

STN 03The oil windowexpulsion below ~3,500 m

What the surveys suggest

Honesty first: the Great South Basin has no proven reserves. It has one measured, undeveloped discovery and a ladder of estimates — each rung bigger and less certain than the one below. Here is the whole ladder, labelled.

tcf-e = trillion cubic feet equivalent (condensate converted at ~6 Bcf per barrel-equivalent basis). “Unrisked” means: the size if the structures work — before multiplying by the chance, often ~10–30% per prospect, that they do. Sources: NZP&M, NZOG/Woodside 2018 farm-out deck, OMV 2019, Crown 2007 backgrounder.

Why anyone is looking again

New Zealand's 2P natural gas reserves, PJ at 1 January (MBIE) — down 44% in two years, the lowest in twenty years of records

The country that shelved the Great South Basin question is now burning imported Indonesian coal at Huntly (imports up 311% in 2024), watching Methanex idle its plants, planning a billion-dollar LNG import terminal — and staring at gas reserves of 731 petajoules, with the Maui field itself expected to stop producing at the end of 2026.

One Kaipatiki-sized discovery — the mean recoverable estimate for the basin's best-mapped prospect is ~5.6 tcf, or about 5,900 PJ — would be roughly eight times the nation's remaining proven reserves. That is the entire argument for drilling, and the entire scale of the gamble, in one number.

STN 04Basement rock−8,600 m · end of the sediment

The South's wider endowment

Hydrocarbons are only the deepest layer of what the southern region could extract, harvest or generate. The same waters and hinterland hold world-class wind, a critical-minerals belt, and one of the largest lignite deposits in the southern hemisphere.

Offshore wind · Te Ara a Kiwa
~10 m/s
mean wind at 100 m in the Foveaux Strait zone — capacity factors of 50–65% are world-class. One of three official offshore-wind regions of interest; a BlueFloat-led consortium has scoped Southland as part of a 5 GW national vision. The Offshore Renewable Energy Act's first feasibility tenders are expected within months.
Southland lignite
6–8 bn tonnes
the biggest untouched fossil resource in the country, valued at roughly $100b in the ground — with at least a billion tonnes economically recoverable, and a $3b lignite-to-urea plant proposed in 2025. Carbon-heavy, and politically contested for exactly that reason.
Otago gold
>5 Moz
produced at Macraes since 1990 — NZ's largest gold mine — while Santana's Bendigo-Ophir project (1.24 Moz reserves, ~$360m GDP/yr projected) heads through fast-track consenting.
Critical minerals
37 listed
on NZ's 2025 critical-minerals list. The southern belt holds rare-earth-bearing sands (Fiordland–Stewart Island rank among the highest-potential REE regions), Chatham Rise phosphate (~25 Mt identified), and titanium-vanadium ironsands. Government target: double mineral exports to $3b by 2035.
The energy anchor
854 MW
Manapōuri, NZ's largest hydro station, feeding the Tiwai Point smelter to at least 2044 — the industrial spine any southern energy build-out starts from. The paused Southern Green Hydrogen project imagined a 600 MW electrolyser here.
The exclusive economic zone
4.1 m km²
one of the largest EEZs on Earth — fifteen times the landmass. Published guesses at its total mineral endowment run from tens of billions to "$500 billion or more"; treat all of them as speculative.

Rock is not wealth.
Wealth is what a country does with the cheque.

New Zealand has earned petroleum money before — roughly half a billion dollars a year at Taranaki's peak, some $11.6 billion of royalties and taxes over the decades. Every dollar went into the year it was earned, and is gone. From here down, this page stops asking what is under the sea, and starts asking the question that actually decides whether any of it matters.

STN 05The control experiment1969 — 2026

The Norway question

Two small, remote, mountainous nations of about five and a half million people found offshore hydrocarbons in the same era — Norway's Ekofisk in December 1969, New Zealand's Maui five months earlier. One of them is now the owner of the largest sovereign wealth fund on Earth. The difference was never the size of the field.

Norway · Government Pension Fund Global
US$2.1 trillion
Per citizen≈ US$385,000
Rulespend ≤ 3% real return
Petroleum tax take78% marginal
Return since 19986.6% p.a.
Share of value that is investment returns, not oil money~71%
New Zealand · petroleum revenue
NZ$0 saved
Cumulative Crown take (Taranaki era)≈ NZ$11.6b
Where it wentthe Consolidated Fund
Royalty regimehigher of 5% AVR / 20% APR
Ring-fenced for the futurenothing
Proof NZ can invest: Super Fund since 200310.1% p.a.

What compounding did for Norway

Government Pension Fund Global, year-end market value, NOK billion (NBIM). First deposit, May 1996: NOK 2 billion.

The Taranaki counterfactual

Illustrative: a ~NZ$250m/yr average Crown petroleum take, 1980–2025 (consistent with the documented ≈$11.6b total) — as received and spent, versus banked and compounded at 5% real

About NZ$45 billion under conservative assumptions — half of today's NZ Super Fund; at the Super Fund's actual realised returns, well over NZ$100 billion. The United Kingdom ran this experiment at scale: £166b of North Sea taxes in the 1980s alone, none saved — a fund started in 1975 on Norwegian lines would be worth £354–850b today (Atkinson & Hamilton 2020; IPPR).

None of this required Norwegian genius. It required three sentences of law: petroleum revenue goes into the fund; the fund invests abroad; the budget may spend only the expected real return. New Zealand already runs a sovereign fund with world-class results — the Super Fund has returned 10.1% a year for two decades. What it has never done is connect a resource to one.

STN 06The model2026 — 2075

Run the fund yourself

Pick a resource outcome — from “only what was already found in 1977” to the Crown's most breathless 2007 marketing — set the Crown's take and the fund's return, and watch fifty years of compounding. Every assumption is on a slider, and the model is documented below.

Maui, the field that powered NZ for 40 years, was 3.8 tcf.

Real NZ$ per gigajoule across the life of production.

NZ's current regime collects roughly 42% of profits (royalties + company tax). Norway takes 78%.

Norway assumes 3%. World equities returned 5.2% real over 125 years. The NZ Super Fund has beaten both.

Annual draw once production ends. Norway's handlingsregelen: 3%.

Fund in 2075
—
real 2026 dollars
Per New Zealander
—
at today's population
Sustainable annual draw
—
every year, in perpetuity
Total Crown revenue banked
—
deposits over 30 years of production

Fund trajectory, 2026–2075

First gas 2035 · 30 years of production · draw begins when production ends

The model is deliberately simple and fully client-side: flat production over 30 years from 2035, Crown take deposited annually, compounding at the chosen real return, spending only after production ends. It ignores development costs to the Crown (it taxes profits, not gross revenue — the take slider absorbs this), price cycles, and exchange rates. It is an illustration of compounding discipline, not a forecast. And the biggest uncertainty is not on any slider: the resource may simply not be there.

STN 07Both columnsthe honest ledger

What it would cost

A survey that only maps the prize isn't a survey. The case against opening the basin is serious, and some of it is unanswerable by economics.

The case for asking the question

  • Energy security is already failing. Gas reserves have fallen two-thirds since 2021; the shortfall is being burned as imported coal at Huntly, with higher global emissions than domestic gas would produce.
  • The counterfactual is not "no fossil fuels." It is fuels produced somewhere else, bought at world prices, with the rents accruing to other treasuries.
  • A fund converts a one-off inheritance into permanent income. Norway's fund now earns more from markets than it ever received from oil; the principle works at any scale.
  • Taranaki showed what an anchor industry does. Oil and gas made it the highest-GDP-per-capita region in the country from 2007 to 2019 — ~23% of regional GDP at peak. MBIE's 2012 modelling put a developed southern basin at +$2.1b a year of national GDP and thousands of jobs.
  • The ban was costed, the cost was paid. MBIE's own 2018 impact statement put forgone Crown revenue at $1.2–23.5b (midpoint ~$7.9b) and warned of emissions leakage — advice the government of the day set aside.
  • Gas is the transition's balancing fuel. A hydro-dominated grid with dry-year risk needs firming; winter 2024's shortage cost the economy over $5b in high electricity prices and closed mills that never reopened.

The case for leaving it down there

  • The climate ledger is global. New Zealand is bound to net-zero 2050; the Climate Change Commission lists the exploration reopening among actions that increase emissions (~14 Mt on official modelling), and the IEA's net-zero pathway has no room for new fields. NZ had to leave the Beyond Oil & Gas Alliance to pass the repeal — against public submissions running 94.5% opposed.
  • This is one of the richest cold-water ecosystems on Earth. Hoiho nests are down ~80% since 2008; Taiaroa Head is the world's only mainland albatross colony; recovering southern right whales breed at the Auckland Islands. NZ's spill response is sized for a 3,500-tonne event — a relief rig is weeks away in Australia, a capping stack is in Scotland.
  • Nine wells say the risk is real. Fifty years, hundreds of millions spent, zero commercial discoveries. Tawhaki-1 burned ~NZ$80m on the basin's best-mapped structure in 2020 and found nothing. Every operator — Hunt, ExxonMobil, Shell, OMV, Beach, NZOG — has walked away.
  • Stranded-asset and taxpayer risk compound every year. The Crown's own timeline is 10+ years from discovery to production — landing new supply in the 2040s against a 2050 net-zero statute. And the Tui field's collapse already cost taxpayers ~$443m in decommissioning; the 2025 Act softened the very liability rules written after that failure.
  • Mana whenua have not signed on. The basin sits in the takiwā of Ngāi Tahu, whose rūnanga asserted taonga species and sought a precautionary approach at OMV's 2019 consent hearing — and the Waitangi Tribunal has twice found the petroleum regime breaches Treaty principles.
  • The industry itself may have moved on. Nearly a year after the reopening, five applications have been lodged nationally — every one in Taranaki, Waikato or Canterbury. Nobody has asked for the Great South Basin. And the South is not desperate: Southland now has the highest GDP per capita in New Zealand on dairy, aluminium and renewables.

If the answer is to drill, the ledger above is exactly why the revenue must not vanish into ordinary spending: a country that takes the environmental and climate risk and then consumes the proceeds within an electoral cycle has made the worst trade available. The fund is not a nice-to-have on top of extraction. It is the only version of extraction that leaves the next century holding something.

STN 08Survey logsources & method

Check the workings

Every number on this page traces to a public source. Where sources conflict — and on a frontier basin they often do — the more conservative or more primary figure is used, and the conflict is noted in the text.

The basin & its geology
  • GNS Science, Cretaceous–Cenozoic Geology and Petroleum Systems of the Great South Basin (Monograph 20, 1999) — gns.cri.nz
  • NZ Petroleum & Minerals, New Zealand Petroleum Basins (2014) — nzpam.govt.nz (part 2, PDF)
  • Oil & Gas Journal, “Great South Basin might hold considerable potential” (1999) — ogj.com
  • Hoffmann et al., Scientific Reports (2021), basin stratigraphy — ncbi.nlm.nih.gov
  • Sahoo et al., Tectonics (2020), rift timing — agu.org
  • Coastline & bathymetry rendered from Natural Earth 10 m public-domain data — naturalearthdata.com
Exploration history & wells
Resource estimates
  • Kawau-1A 461 Bcf original estimate; basin statistics — NZP&M NZ Petroleum Basins (above)
  • NZOG SEAPEX farm-out presentation (2018): Kaipatiki prospect, PRMS unrisked — seapex.org (PDF)
  • OMV mapped leads ≈3.6–3.7 bn boe (2019) — odt.co.nz, rnz.co.nz
  • “Up to ten times Maui” — Crown 2007 FAQ (above), stated there as unproven
  • MBIE petroleum reserves data (gas decline to ~605 PJ) — mbie.govt.nz
The wider endowment
Sovereign wealth funds & the model
Policy & the 2025 reopening

Method. This page was compiled in July 2026 from the public record. Resource figures are quoted with their class — found, mapped, or marketed — because on a frontier basin the difference is the whole story. The fund model runs entirely in your browser; its assumptions are stated beside it and its arithmetic is one loop of compound interest. Nothing here is investment, legal or geological advice, and the page is not affiliated with the Crown, any iwi, or any company named on it.