After days of confusion, the West Australian government has confirmed it is now actively investigating repeated large methane emissions from Chevron's Gorgon gas project off the state's Pilbara coast.
The Department of Water and Environmental Regulation (DWER) was initially unclear on whether it had jurisdiction over the plumes, which had been observed by a United Nations-linked satellite for the past year.
But a government spokesperson said DWER was "working hard" to establish the cause of the emissions, and engaging with Chevron to determine the appropriate response.
"It would be inappropriate to speculate while the investigation is underway,"
the spokesperson said.
Chevron's Gorgon LNG plant is among Australia's largest. (Supplied: Chevron)
The Gorgon liquefied natural gas (LNG) plant on Barrow Island is one of the biggest in Australia, boasting a capacity of 15.6 million tonnes per year across its three processing trains.
All of the LNG is shipped overseas. Gorgon hit its 2,000th cargo milestone in February.
About 300 terajoules of Chevron's remaining natural gas is kept for domestic use under the state's reservation policy, which the company says generates enough electricity for 2.5 million households.
In April, the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) accepted Chevron's plans to install a subsea compression station and other infrastructure to maintain production at Gorgon over another 40 years.
Since November last year, five consecutive passes by the Tanager-1 satellite have detected huge methane clouds emerging from the industrial complex.
The most recent posted an emissions rate of 7.8 tonnes of methane an hour near Gorgon's acid gas removal units, making it the highest methane emitter in WA.
Chevron did not comment on the state investigation. ( ABC News: Keane Bourke )
Methane is a much more potent greenhouse gas than carbon dioxide and responsible for about 25 per cent of global warming.
The UN warned Chevron about its emissions in July last year and as recently as August this year.
The multinational gas giant has not formally provided feedback to the alerts.
Chevron told the ABC it was corresponding with the UN over its data, but did not comment on the state's investigation.
WA Greens MLC Sophie McNeill said it was "embarrassing" DWER was not monitoring the emissions and remained noncommittal after they came to light.
"We know that this Labor government has never fined gas companies for these kinds of unauthorised leaks of pollutants," she said.
"This incident proves that the whole system needs to be overhauled."
'A matter for the state regulator'
Pressed during Senate Estimates by independent senator David Pocock, the federal Department of Climate Change, Energy, the Environment, and Water (DCCEEW) said repeatedly that the oversight of emissions was state-based.
"We're aware of media reports over the last couple of days," said Hew Atkin, DCCEEW's gas and liquid fuels division chief, on Monday.
"My understanding is that's a matter for the state regulator."
Mr Pocock raised the large, unexplained emissions during Monday's Senate Estimates hearing. (ABC News: David Sciasci)
Mr Pocock questioned the lack of involvement from the Commonwealth.
"How on earth is this program going to be successful if we don't know about a reportedly massive, unexplained release of methane over the last year or so?"
Chevron is required to report its emissions through the National Greenhouse and Energy Reporting Scheme. The numbers are published annually.
Australia's current legislated target is to reduce emissions by 43 per cent from 2005 levels by 2030 and achieve net zero emissions by 2050.
According to the UN's International Methane Emissions Observatory, Australia is home to two of the world's top-35 methane emitters as of November.
Both are metallurgical coal mines, Queensland's Moranbah north coal mine, operated by Anglo American, and New South Wales' Appin coal mine, operated by GM3.