The ExxonMobil oil company has been fined £2.8 million for failing to report greenhouse gas emissions from its chemical plant in Scotland.
It is the largest fine for an environmental offence in British history.
The Scottish Environment Protection Agency fined the company in 2010-11 for not reporting 33,000 tonnes of carbon dioxide emissions from its Mossmorran ethylene plant in Fife.
But the fine was not publicised by Sepa at the time and only came to light in a report published last week, which revealed ExxonMobil had identified pollution it did not report in 2008.
EU laws place strict rules on companies for accurately reporting emissions, with 100-euro fines (£83) for every tonne they miss.
The money from the fine has been passed to the Scottish Government to fund environmental projects.
Four other companies have also been penalised for "underestimating" greenhouse gas emissions from plants in Scotland: Dow Chemical Company (Grangemouth), Tennent Caledonian (Glasgow), Pernod Ricard (Glasgow) and FMC BioPolymer (Girvan).
Commenting on the fine, WWF Scotland director Richard Dixon said: "The whole point of the European trading scheme is to limit the total climate pollution coming from industry. So it is quite right that fines should be high for those who fail to comply.
Scottish Green party co-leader Patrick Harvie said: "This massive failure to accurately report is just the latest in a long, sorry tale of complacency by the oil industry.
"We need up-to-date, accurate reporting if we are to protect our environment and crack down on those contributing to climate change."