Tui operator Australian Worldwide Exploration has spent much of the past three days meeting with the other Tui partners, Umuroa operator Prosafe, Maritime New Zealand, the Taranaki Regional Council and other groups associated with the clean-up operation.
Last week AWE supplied a sample of Tui crude to Maritime NZ for analysis and comparison with the degraded oil that washed up over a 10km-long stretch of Taranaki coastline in the form of tar balls.
It now appeared that degraded oil had come from the Umuroa and was related to the discharge of contaminated produced water from the FPSO on October 21, AWE managing director Bruce Wood said in New Plymouth.
He also said it appeared there were no physical or mechanical defects relating to the Umuroa and the discharge had been an operational or procedural problem.
New Zealand's largest private energy company, Todd Energy, is helping with the Tui clean-up.
Todd's chartered tanker Savannah loaded the rest of the contaminated water from the Umuroa on Monday night and then sailed to Port Taranaki. It is now sitting off the New Plymouth port waiting to discharge its cargo into a ballast tank often used by tankers as part of their clean-up operations.
Earlier this year Todd Energy chartered the Savannah for an initial two-year period to handle all its shipments of Taranaki crude and condensate.
The incident was AWE's first environmental blemish in operating several fields in Australia and Tui in New Zealand.
The Tui project is about 60km from the affected Taranaki coastline.
The Tui partners are operator AWE (42.5%), Mitsui E&P NZ (35%), NZOG (12.5%) and Pan Pacific Petroleum (10%).