Researchers have revealed the alarming methane emissions from one of what may be 130,000 coal exploration boreholes across Queensland.
The University of Queensland research team took the readings as it monitored the abandoned borehole dubbed a "methane super emitter" for a week in southern Queensland's Surat Basin.
"We measured it to be releasing 235 tonnes of the greenhouse gas into the atmosphere each year," said UQ Associate Professor Phil Hayes.
"In terms of climate impact, that's on par with emissions from 10,000 new cars driving 12,000 kilometres each, every year.
"This borehole is one of an estimated 130,000 in Queensland where the quality of sealing by coal explorers is unknown."
His colleague Sebastian Hoerning said there were thousands of abandoned boreholes across the state.
Another borehole they monitored leaked methane causing a geyser in a small pond before it was sealed.
"While the majority of these boreholes won't be emitters, our measurements show they could be a major source of greenhouse gas emissions that is currently unreported," Dr Hoerning said.
The researchers said sealing the worst offending boreholes would be a cost-effective way of quickly reducing Queensland's greenhouse gas emissions.
The UQ research was published in Science of the Total Environment.
Companies undertaking coal exploration must communicate the location and type of every borehole created in Queensland.
A number of measures must also be taken when abandoning a borehole including plugging it under state legislation.
The Queensland government said legacy coal exploration boreholes were "more complex".
"These would have been drilled and abandoned prior to government introducing more stringent and detailed borehole drilling and abandonment requirements," a Department of Natural Resources and Mines spokesperson said in a statement.
"In many cases, these old boreholes may not have been properly mapped and the resource company that drilled and abandoned them no longer exists.
"When the department becomes aware of a significant community health and safety risk associated with a legacy coal borehole, it is assessed to determine whether remediation is required."
The Queensland Conservation Council called on the state government to complete a borehole audit paid for by coal royalties.
It feared if just five per cent of the state's 130,000 boreholes leaked the same amount as the one featured in the UQ research it would be the equivalent of 65 million cars.
"This research is the tip of the methane iceberg for Queensland," the council's Charlie Cox said.
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