Oil could reach Raglan shores if exploratory drilling caused a spill, according to recently-released documents, but a spill is nevertheless considered "extremely unlikely".
However, Greenpeace maintains the information proves drilling shouldn't have gone ahead.
In late November, drill ship Noble Bob Douglas began working on an exploratory oil and gas well 204 kilometres west of Raglan - the deepest undersea well ever attempted in New Zealand.
Oil and gas exploration company Anadarko's plan for dealing with discharge during the drilling was released yesterday under the Official Information Act.
The plan, prepared by Environmental Resources Management, said while a spill could have significant environmental and social impacts, one was unlikely to occur.
Given Anadarko's prevention and response measures, any impact would be "as low as reasonably practicable".
Earlier this week, lawyers for Greenpeace argued in the High Court that the Government's Environmental Protection Authority should have seen the documents before giving the drilling programme the go-ahead.
Chief policy adviser for Greenpeace Nathan Argent said the Government and oil lobbyists had tried to stop the New Zealand public from finding out about what could happen in an oil spill.
"The industry's own data shows that oil could end up on our beaches. And there's more than a hint that the Government and the oil lobbyists colluded to keep this secret," he said.
"The whole government process around deepsea oil drilling has swung between utter farce and total shambles."
Part of the discharge management plan was modelling to find "likely pathways and possible locations of shoreline beaching" of oil for several spill scenarios.
The Raglan area would be most at risk of finding oil on the shore in the summer period, with a medium, or 1 to 3 per cent, chance.
Across all the simulations, the fastest time for oil to reach Kiwi shores was 67 hours, in the autumn, when 66 per cent of simulated spills beached.
Anadarko's New Zealand corporate affairs manager Alan Seay said the modelling was based on no intervention for 35 days, what would occur "if you just stood back and let it happen".
Cases of oil reaching shore referred to any quantity of hydrocarbons, "even if it's just a teaspoonful".
The modelling assumed oil was being lost at 12,000 barrels per day, which he said was the best guess at a worst-case scenario, given what Anadarko expected to find in the area.
Tier one spills would be dealt with by Anadarko on the spot, Mr Seay said, but Maritime New Zealand's Marine Pollution Response Services would take charge in the event of a larger spill.
"They can commandeer Anadarko's equipment and equipment from other people and direct us to bring equipment in from all around the world to deal with it, but Maritime New Zealand takes over the running of it," he said.
"Anadarko would be providing everything, but the people running how the incident was dealt with would be Maritime New Zealand."
Anadarko also has a contract with Oil Spill Response Limited, an international industry-owned co-operative which can provide necessary equipment which New Zealand may not have.
- © Fairfax NZ News