Mobil did not know how much the clean up had cost it to date as it was an ongoing process, so the costs had not been compiled.
Mobil believed about 1500 litres had leaked into the harbour but said "it is difficult to make an accurate assessment of the volume lost given the circumstances".
The pipeline which leaked the oil had been shut down and would not be used again until Mobil was sure it was safe and everything was done to ensure it would not leak again, Ms Potts said.
Ships had been refuelled at a separate, second refuelling spot since the spill.
The Bay of Plenty Regional Council's on-scene commander, Peter Buell, said there was still more work to be done before they were happy with how clean the environment was.
"Just over 30 tonnes of oiled waste has been recovered," he said.
"While the majority of work has been completed there is still more to be done to ensure we reach an appropriate end state."
Labour environment spokeswoman Megan Woods visited Tauranga yesterday to be briefed on progress in the clean up of the latest oil spill.
"Every conversation I've had, it's very evident how deep the Rena scars are. People here understand the impact of an environmental disaster locally ... It's their home and their backyard."
The investigation into how the spill happened would provide the basis of how to prevent similar disasters in the future.
Looking at the most up-to-date technology used in ports around the world could help to pave the way for the Port of Tauranga's future infrastructure, she said.
Many of her questions relating to what caused the spill and how it could be prevented could not be answered by local authorities yesterday as it was too early in the investigations, she said.
Seeing the marks of the spill on the local environment reminded her that there were personal implications for locals who used the water for recreation or a food source, on top of the obvious economic implications.
"I'd never seen an oil spill before and it's pretty confronting. Seeing the grass covered in such viscous sludge. That body of water has such importance to people."
She would be keeping in touch with the regional council to ensure her questions were answered.
Tauranga oil spill
April 27: Oil leaks into the harbour from a damaged pipe
April 27: Oil reaches estuary and washes up on Maungatapu properties
April 28: Mobil takes responsibility for pipe and apologises for the spill
May 1: Mobil estimates 1500 litres of fuel has leaked into the harbour
May 1: Oiled debris washes up at Pilot Bay
May 2: Tauranga MP Simon Bridges visits the spill
May 4: 21 tonnes of oiled-waste collected to date
May 4: List MP Clayton Mitchell calls for Mobil to be prosecuted
