On top of the record high prices already experienced in 2011, Brisbane motorists would pay up to 10cpl more for unleaded fuel under a carbon tax according to a new report.

RACQ's latest monthly fuel price report revealed Brisbane motorists paid an average price of 144.9 cpl (cents per litre) in March - the highest monthly average since July 2008 (151.4cpl) and the third highest monthly average on record.

RACQ executive manager for public policy, Michael Roth, said prices had risen 6.5cpl since February. He warned that a number of international factors, combined with the imposition of a carbon tax on fuel, would push them even higher.

"Political unrest in Libya has forced prices up and they will remain high while the conflict continues," Mr Roth said.

"Further pressure on the oil price is expected following the tsunami in Japan, as demand for oil and gas will increase to replace lost nuclear energy.

"Fortunately, fuel prices are being buffered by the Australian dollar, which is the strongest it's been since it was floated in 1983," he said.

"But if the carbon price is introduced and the Australian dollar goes down motorists will be facing significantly higher fuel prices than today."

Mr Roth said the RACQ was calling for a reduction in fuel taxes to compensate motorists for the impact of a carbon price. There were fairer and more effective ways to reduce carbon emissions than hitting motorists with higher fuel prices.

The RACQ March fuel price report showed that ULP in Brisbane was more expensive than Sydney (143.2cpl), Melbourne (141.7cpl), Canberra (143.9cpl), Perth (142.0) and Adelaide (137.2).

The weekly price cycle was steady throughout March, with Saturday the cheapest day to fuel up before prices rose on Sunday.