Petrol prices have jumped around the country in the past week because of higher oil prices and the falling Australian dollar.

Figures from the Australian Institute of Petroleum show the national average price of unleaded petrol rose by 5.4 cents to 142.9 cents per litre last week.

The rise was the second biggest weekly jump in the past four years, and CommSec economist Savanth Sebastian says there is no reprieve on the horizon.

"Motorists are being hit with a double whammy - higher fuel prices globally and also a falling Australian dollar," he explained.

"That means the domestic pump price is going to rise over the next couple of weeks."

Motorists can expect higher petrol prices in the weeks ahead, because the lower Australian dollar is pushing up the cost of imported fuel.

Mr Sebastian says, while the falling dollar may bring some relief to exporters and trade-exposed sectors, it will mean more pain at the pump for motorists if the currency keeps going down.

"Had the Aussie been holding at 103 motorists would be actually be saving about 7 cents per litre off their fuel bill, so it really does highlight that the Australian dollar plays a huge impact in ensuring that motorists save at the pump," he said.

"So going forward I think we're really looking at the Aussie holding around these sorts of levels. Certainly any further downside risk to the Australian dollar and motorists will be paying more at the pump."

CommSec says the rise in petrol prices is also likely to have a negative impact on consumer sentiment.

Mr Sebastian says that is because the majority of households own cars and will need to put more of their weekly budget aside to cover the increasing cost of fuel.

"Keep in mind, over the next couple of weeks, it's very likely that fuel prices will probably rise by about 3 to 4 cents per litre, so there's still substantial increases to come," he forecast.

"Petrol is the single biggest purchase made by households on a weekly basis, and I think it's not just that petrol prices are rising but the extent of the price rises can have a huge impact in sapping consumer confidence."