A man was arrested after the discovery of a fuel laundering plant and illegal filling station in Co Tyrone, customs officials said.
The plant, capable of producing 14,000 litres of illicit fuel a week, evading £10,000 in duty, was found in the Pomeroy area.
Officers from Her Majesty's Revenue and Customs (HMRC) assisted by the PSNI carried out searches at a private residence on Wednesday.
In one shed at the back of the property HMRC found and dismantled a laundering plant. Pumps and other equipment believed to have been used to sell illicit fuel at a reduced price were removed for examination.
Pat Curtis, national oils co-ordinator with HMRC, said: "Buying illicit fuel not only funds crime but supports and encourages these dangerous activities within our communities.
"The only winners are the criminals who are profiting at the expense of honest businesses. They are endangering the future viability of our legitimate fuel retail service."