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 told the Bay of Plenty Times.
"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.
In some senses, the volume itself is irrelevant, it's whether the response is appropriate.
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.
Read more: 'Shaggy the shag dies after being coated in oil
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."
Read more: Corroded Mobil oil pipe blamed for harbour spill
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.
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.
"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.
Image 1 of 15: Regional council workers Nathan Capper left and Reece Irving tying up bags. Photo/George Novak
"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.
Penguins spotted with oil were seen around Mauao Island on Wednesday night and it was feared there could be more wildlife affected by the oil spill.
Mauao Area Wildlife Trust director Julia Graham said there were three penguins with oil spots while another had its chest covered, and she suspected more penguins and wildlife could be contaminated following the oil spill in Tauranga Harbour on Monday.
"The oil wasn't affecting them in any way, shape or form. It hadn't gone all the way through to the skin, so they were still water proof, they were still happy, they were still healthy." Teams of 20 to 25 people from Mauao Area Wildlife will continue to scout around Mauao and Leisure Island.
We ask Peter Buell, Bay of Plenty Regional Council's on-scene commander, questions about Monday's oil spill. These are his answers:
How long will it take to find out how much oil was spilled?
While it would be useful to know the amount of oil spilled, this information isn't critical to our response. We completed rapid shoreline and on-water surveys to give us a clear picture of the scale of the oil spread and enabled us to put our response plan, trained staff and specialised equipment in place effectively.
How much waste from the oil spill has been removed so far?
By the end of [Wednesday] we had collected approximately seven tonnes of oil-covered sand, vegetation and other debris.
What clean-up operations happened yesterday? What's happening today?
Approximately 70 staff, volunteers, iwi and contractors have continued work at Maungatapu, Tauranga Bridge Marina and the port to collect oil using sorbent booms, pads, skimmers and shovels.
How much oiled wildlife has been found to date? How many have died?
There have been just two shags and one penguin captured and needing treatment for oiling. The penguin has recovered and will be released this evening.
Is there oil on the harbour bed? Where? What does this mean for the environment and marine life?
Scientists from Bay of Plenty Regional Council and University of Waikato accompanied by iwi have been investigating this and taking samples with a particular focus on shellfish and sea grass. It will be a few weeks before analysis of the first sampling round is completed.
What ongoing effects is the regional council preparing for?
We continue to be focused on cleaning up as much oil as possible, using every appropriate method. Our science team are starting to investigate what the long-term impacts (if any) might be.
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