Economists say the high Australian dollar is keeping petrol prices low in the lead up to Christmas.

Figures from the Australian Institute of Petroleum show the national average retail petrol price fell to 143.2 cents per litre in the past week.

Commsec economist Savanth Sebastian says the global petrol price has fallen in the past few weeks, but the strength of the local currency means it is even lower in Australia.

"At the moment it really comes down to the Australian dollar," he said.

"We've seen that the global fuel price - the Singapore unleaded price - is effectively tracking sideways, but the Australian dollar's strength since early October has been quite phenomenal.

"In fact that movement in the Australian dollar has effectively saved motorists about five cents a litre every time they fill up."

Mr Sebastian says petrol prices will dip this week and in the new year.

"Mostly we're seeing across the eastern seaboard that the low point in the cycle is in the next couple of days," he said.

"I think for motorists if you do fill up in the next couple of days, and in a fortnight's time you'll probably see prices about two to three cents cheaper than where they are now."