Four men have been arrested after a substantial fuel laundering plant was discovered.
A man from Meath and another from Louth were detained along with two others from Northern Ireland after the illegal oil operation was found.
The laundering plant was unearthed in Knightstown, Co Meath, by Customs and Garda officers.
Illegal fuel was being put through the specialist cleansing machines when the officers raided the site.
Some 30,000 litres of laundered fuel, 12,000 litres of leftover sludge, two tanker trailer units and four vehicles were seized at the plant.
Officers also dismantled and seized some other ancillary equipment.
Customs said the plant had the capacity to launder an estimated 7.8 million litres of fuel a year with a potential loss to the Exchequer of approximately 4 million euro.
Investigations are ongoing.