Fuel laundering is linked to organised crime gangs, which are often paramilitary, a judge has said.
The remarks came during a case at Dungannon Magistrates Court involving the rental of a barn found equipped with tanks containing 2,800 litres of illicit fuel.
It followed a heated exchange in court where District Judge John Meehan warned a defence barrister not to "provide a personal judgment on his client's honesty".
Kevin McKeown (45), of Drumhubbert Road, Dungannon, was convicted of knowingly being involved in taking steps with a view to fraudulent evasion of duty excise on hydrocarbon oil.
He steadfastly maintained knowing nothing of a fuel laundering operation on his property, and stated he only gained financially through rental of the barn.
A large amount of equipment was seized in the raid in March 2015.
During a contested hearing, McKeown was adamant he knew nothing of what went on in the shed, and never went into it. He referred only to "persons unknown", and contended he received £30 per week in rent.
But District Judge Meehan rejected this, and ordered a conviction, commenting McKeown could not have missed what was going on, given the delivery and running of extensive equipment 80 yards from his home.
The case was adjourned for pre-sentence reports, and in these McKeown accepted he had lied to the court during the contest. A defence barrister said his client "gave an entire account to the court which was misleading".
However, while Judge Meehan noted the admission, he was critical of McKeown's continued stance that he made little money from the operation.
The judge said: "The illegal laundering of fuel took place at that property for many years.
"The defendant claimed he didn't know there was a barnful of equipment next door.
"This was an entirely deceptive operation. We only know how much the defendant claims to have made.
"We do not know the overall loss to the taxpayer. There was a highly-sophisticated operation going on in that barn."
The defence barrister contended McKeown could not be considered criminally sophisticated, but rather was used by others.
He said: "My client was not in the barn, so he could not have been involved in fuel laundering. There were no fingerprints or DNA found on the equipment. He made only £30 per week."
Judge Meehan replied: "I'm not interested in that. He made the premises available for illegal activity. That puts him into a highly criminal subset."
The defence barrister persisted: "My client says he made only £30 per week."
Judge Meehan said: "You are acting for someone who swore on the Bible to tell the truth, then proceeded to lie throughout the entire hearing. I am not inviting you to provide personal judgment on his honesty."
The barrister added: "I cannot detract from my client's instructions."
Imprisoning McKeown for three months, Judge Meehan concluded: "It is important to deter others from supplying premises for this kind of illicit activity."