Spokesman Peter Khoury said the motoring group was expecting to see the average price for a litre of unleaded petrol in Sydney fall to about $1.21 - about 13¢ cheaper than Tuesday's prices.

He expected Wollongong to follow the trend.

"We think prices will drop over the Easter long weekend," Mr Khoury said. "If they don't fall in time for when people are going away, they will fall over the long weekend."

He predicted the price drop after looking at the petrol pricing cycle, which is falling, and taking into account factors such as the value of the Australian dollar and the oil prices in Singapore against which Australian prices are benchmarked.

Mr Khoury said the price drop would be strongest in Sydney, where there were more independent stations. But he expected Illawarra drivers would also benefit.

"What is good for Wollongong is the region tends to follow the cycle in Sydney, and that's been going for the last six months," Mr Khoury said.

"That's all the more reason for people in Wollongong to do a bit of research before they fill up. If this trend continues of Wollongong following Sydney, what we want our members to be doing is filling up when the cycle is at its lowest."

Mr Khoury advised Illawarra motorists who were going away this long weekend to hold off filling their tanks until later in the week, when the prices were likely to be falling.

Those travelling down the coast or to inland areas should fill up before they left, as Wollongong prices were certain to be lower than those in smaller areas.

There is an urban tale that petrol prices always go up just ahead of a long weekend, but Mr Khoury said that was not a trend the NRMA had seen recently.

"We have seen that happen in the past but it hasn't happened in a while," he said.

"You'd have to go back about three Christmases to see an example, when all the trends were pointing towards prices going down and they suddenly went up.

"We haven't seen that happen for a while and I would be most shocked if it happened now."