Refining NZ first revealed that there was a problem with its pipeline to Auckland last Thursday when it posted about it on Facebook but it was not until Sunday that the full extent of the problem became widely known, raising questions as to when the company should have advised the share market.
The rupture of its 170km-long pipeline, through which it pumps aviation fuel for use at Auckland International Airport, has caused widespread disruption at the airport through flight cancellations and postponements.
Refining NZ shares have gone from $2.57 last week to $2.44 today, when the company made its first official announcement to the NZX.
An investor has complained to the authorities about Refining NZ's slowness to tell the market about the pipeline leak which has led to travel disruption amid a shortage in aviation fuel.
Peter Wakeman, who owns shares in Auckland Airport, said he was concerned people were trading shares last week without full knowledge about the potential impact on the company and other listed companies such as the airport and airlines.
"It is unbelievable for Refining NZ to not make the disclosure until Monday morning," he said.
Wakeman said he had complained to the NZX and the Financial Markets Authority about the delay.
Stock exchange operator NZX has said it is in talks with Refining NZ regarding its announcement about the pipeline leak.
Listed companies have an obligation to continuously report anything that may have a material impact on them.
Asked if the NZX was looking into the timing of the announcement a spokeswoman said it was "engaging with Refining NZ on this morning's announcement regarding the Wiri pipeline leak".
Refining NZ chief executive Sjoerd Post was unavailable for comment to the Herald on the disclosure issue today.
In last Thursday's Facebook post, Refining NZ said: "Hi everyone. Just to let you know that earlier this afternoon we spotted a leak of jet fuel on a section of the Refinery Auckland pipeline near Ruakaka. We've isolated and contained the leak and our crew is busy carrying out a recovery and repair operation.
"The Fire Service has a cordon in place and as a precaution we've put a family who live nearby into a local motel.
"We're working with the oil co's [sic] to ensure that fuel supplies aren't unduly impacted. An early estimate is that pipeline will be out for the next two days.
"Finally, the refinery will continue to operate while we get the pipeline back up and running," it said then.
In its statement to the NZX today, Refining NZ said it was too early to estimate accurately what the financial impact of the rupture would be, but it expected that its revenue would be affected by NZ$10-$15 million.
The company is New Zealand's only oil refinery and the leading supplier of refined petroleum products to the New Zealand market, including petrol, diesel, aviation fuel and other products.
Almost half the company's fuel production travels via its purpose-built 170km pipeline to Wiri in South Auckland for storage and subsequent distribution by road.
The balance is transported by coastal tanker to destinations throughout New Zealand.
As well as being big customers, major oil companies BP, Mobil and Z Energy are significant shareholders in the refinery.