Tauranga-based MP Clayton Mitchell has blasted Mobil's "spin doctoring" over how much oil has leaked into the harbour.
The New Zealand First MP said finding out how much fuel had ended up in Tauranga Harbour should be simple.
"They will be able to work that out. They aren't telling us because they are trying to spin it to make it sound like it's not a major deal when it is a major deal," he said.
"It's just filibustering. They are spin-doctoring it."
But a Mobil spokesperson said the amount of oil would be hard to determine because the leak in the pipe was located before the fuel meter.
Mobil has said it checked the pipelines every three months, but Mr Mitchell said quarterly checks were unacceptable.
Systems needed improving to ensure such a leak never happened again, he said.
"The impact this will have on the tourism sector - we've all felt the effects of the back end of the Rena. Now we're again being hit with images of oil in our beautiful harbour."
Mobil said a meter measured how much oil went through the pipe into ships being refuelled - but the leak occurred before the meter.
This made estimating how much oil had spilled into the harbour much harder to calculate, the spokesperson said.
"In some senses, the volume itself is irrelevant, it's whether the response is appropriate. In this case, we can be absolutely confident the Bay of Plenty Regional Council has manned an excellent response."
The oil leaked from two holes about 4mm in diameter on a 3m-long pipeline that branches off a main pipeline along Mount Maunganui Wharf. The network carried heavy fuel oil for ships.
It would be a week or two before engineers could estimate how much fuel was spilled.
The pipes were checked last month as part of a quarterly maintenance programme, the spokesperson said.
"The March test didn't identify any issues so the investigation is trying to understand why it happened. The pressure test conducted would have picked up that kind of problem."
Mobil believed Tauranga was one of only two ports in the country to have such a pipeline.
"There are not that many fuel lines in New Zealand that carry bunker fuel. We have shut down the whole pipeline system to the wharf and are looking at all sections of pipeline that run off the main line and testing those.
"We won't be putting them back into service until we are absolutely sure there are no issues."
The spokesperson said the pipeline system would continue to be used.
Tauranga MP Simon Bridges, when asked if it was safe to use a system that could develop a leak in one month, said in a written statement: "Maritime NZ is currently providing Bay of Plenty Regional Council with technical assistance to assess the processes used by Mobil in the case. This will include the inspection regime for the pipe and how this was administered.
"The council has stopped this line being used until the investigation is complete."
Mr Bridges said it was not feasible to use portable bunkering for a large ship.
"For instance, in this case, the ship was taking on 500 tonnes of heavy fuel oil, and a road tanker carries only around 20 tonnes."
Green Party conservation spokesperson Eugenie Sage said the spill highlighted how damaging oil and gas exploration could be on the environment.
"Mobil can't tell us how much oil has been spilt from their corroded pipeline into Tauranga Harbour. It begs the question as to how companies would cope if there was a larger spill from deep-sea oil exploration -- a particularly risky endeavour."
Ms Sage said it had been five years since the Deep Water Horizon oil spill in the Gulf of Mexico, but the impact on wildlife was still being felt.
"When the Rena ran aground off the Bay of Plenty coast, the impact was overwhelming. Some 2000 dead birds were found, and up to 20,000 birds are thought to have been killed. Taxpayers paid nearly $48 million in the aftermath of the disaster," she said.
- By Sonya Bateson of the Bay of Plenty Times
