The long-weekend petrol price gouge by the major oil companies has prompted Queensland Nationals Senator Barnaby Joyce to step up his calls for Trade Practices law reform.

"The ACCC should be granted greater investigatory powers against cartels including phone tapping powers.

"This should be backed up with fines and criminal sanctions which deter executives from participating in price fixing," Senator Joyce said.

"The oil companies are obviously acting as an oligopoly. They work together in a formal fashion when they sell fuel to each other at the terminal gate; remember at best there are only two companies refining in a given State. Some states have just one company refining and many have none.

"Do you know many other industries where major competitors sell product to each other at agreed prices that allow them to make a profit? I thought there was another word for that type of conduct.

"Seeing they agreed at a terminal gate level on price structure, it is not a great leap to agree at a retail level. Only a fuel truck separates the two locations."

Senator Joyce said the 'test of market power' provision under the Trade Practices Act was not capturing duopoly or oligopolies and the lack of phone tapping powers made it difficult to prove cases in court.

"As I have previously stated, you virtually need a signed statutory declaration from all participants saying they colluded to prove collusion.

"The phenomenon of petrol prices rising on weekends has long since lost its sense of mystery to the Australian consumer. They know exactly what is going on and they want it fixed.

"Trade Practices law reform is the ultimate solution. Even if we were to reduce excise, I am completely confident it would only be a matter of time before the prices went back up to their previous position only this time the money would be going straight to the oil companies.

"I would rather the money go to our roads than to Dutch, US or British shareholders.

"The Nationals have consistently argued for trade practice law reform and we will continue to do so in order to address the injustices and excesses of those who manipulate their power to extract an unreasonable premium from the consumer whilst, at the same time, inhibiting the right of the Australian citizen to go in to business against them." Senator Joyce said.