Three companies found guilty of spilling 10,000 litres of petrol have been ordered to pay the heaviest fine imposed in a regional council case in Auckland.

Petrol Alley Services (GAS), URS New Zealand and Brown Bros (NZ) were found guilty in the Auckland District Court over a fuel leak from a petrol station in Line Rd, Glen Innes.

The companies have been ordered to pay a fine of $160,000, as well as court costs of $80,000.

The court has also demanded an investigation of the fuel which remained in the ground, and the companies could be forced to pay a further $200,000 for a clean-up.

Prosecutor Auckland Regional Council said the charges and fine sent a strong message to large companies to be tighter in their procedures.

"The fines were due to the seriousness of the incident," said lawyer Janet Whiteside. "The whole industry needs to take a message from this sort of incident so it can't happen again."

The three companies had claimed they were not at fault and had done everything reasonable to stop the petrol escaping.

Engineering consultancy URS hired contractors Brown Bros to test the site for contamination by former owner Caltex.

Brown Bros accidentally drilled a hole the size of a 50c piece in a fuel line used to carry 91 octane.

The spill occurred when new owners GAS reopened the petrol station with the help of another company, Fuelquip.

Fuelquip - which had already pleaded guilty - tested the fuel lines, unaware of the hole. The petrol leaked into the Ruapatoka Stream, 75m away, killing some wildlife.

GAS had argued that the chance of a company such as URS or Brown Bros drilling a hole in a fuel line and not repairing it was extraordinary, and the company could not have foreseen it.

URS and GAS each argued they could not have been expected to predict mistakes by the other.

Judge Fred McElrea ruled that URS and Brown Bros did not take necessary precautions to prevent a fuel leak, and that GAS failed to order the testing of the fuel lines.

GAS paid about $205,000 in cleaning up the site after the spill in December 2007. The judge ruled that this cost should be shared by the other companies.

GAS lawyers said 200,000 litres of petrol and oil had been sucked from the stream and the service station, and experts had said there was no need for further cleaning-up.

But the ARC believed there were still pollutants in the soil, and successfully called for further remedial work.