Australian petrol prices are set to drop four cents a litre in coming weeks following the Brexit vote and turmoil in global markets, says the NRMA.

Average prices should drop to $1.11 by the end of the week and continue to fall about four cents in coming weeks, according to NRMA spokesman Peter Khoury.

"That has happened as a result of the panic selling from last week," he told reporters in Sydney on Monday.

Motorists across the country should see the effects of the drop in world oil prices in about seven to 10 days, especially if the instability continues, he said.

Mr Khoury advised motorists to wait for the price drop before filling up their tanks.