AWE yesterday afternoon said that while Maritime New Zealand was still further testing the tar balls, the Tui joint venture accepted that the source of the pollution was the accidental discharge of oil-contaminated produced water from Tui’s floating storage, processing and offtake vessel, Umuroa, on October 21.

It said the joint venture would meet all costs associated with the clean-up. These costs were not expected to be material.

AWE said immediate measures had been taken to guard against any repeat of this incident, though it did not specify what those measures involved.

Government authority Maritime NZ has still to decide if any further action should be taken relating to the accident.

The tar balls and contaminated sand were found a few days after October 21, dotted along a 10km stretch of coastline, about 60km from the Tui project.

According to AWE, human error, rather than equipment failure, appeared to be to blame for the discharge.

Production operations had continued uninterrupted and the integrity of the production wells and facilities was not in question, the company said.

The Tui partners are operator AWE (42.5%), Mitsui E&P NZ (35%), NZOG (12.5%) and Pan Pacific Petroleum (10%).