Put it down to market competition, said RACV vehicle engineering manager Michael Case.

The average fuel price for unleaded fuel in Horsham for the seven days to January 2 was 156.8 cents a litre, compared with 151.9 cents a litre at Ararat bowsers.

"The price difference is almost certainly to do with local competition," Mr Case said.

"There is no other reason why the price of fuel should vary by almost five cents between Horsham and Ararat."

But Mr Case said Wimmera residents were still better off filling up closer to home if they were planning on driving to Melbourne, where unleaded fuel prices had peaked at 164.9 cents a litre.

"Unlike regional centres, Melbourne and nearby cities have a fuel price cycle," he said.

"We've just started a new cycle with a peak price of 164.9."

Mr Case said many motorists believed fuel prices spiked before public holidays such as Christmas or Easter.

"But our research shows that's not necessarily the case," he said.

Mr Case said fuel outlets negotiating the balance between customer volume and revenue, while staying competitive, was the most likely factor.

In metropolitan areas, Mr Case said there was a noticeable trend in the ebb and flow of petrol pricing called the fuel price cycle.

"This price cycle peaked about a week before Christmas, was on its way down through the Christmas period through to the new year, and spiked up again at the beginning of the new price cycle," he said.

Mr Case said changes in the price of petrol in regional areas was more likely to be determined by amounts wholesalers were paying for petrol.

"Any change to the price of petrol in regional centres is usually related to global effects on fuel prices," he said.

Australian Institute of Petroleum records show petrol prices in Horsham were higher during the week of December 15 than they had been in the 40 weeks prior, peaking around 156.6 cents.

In Ararat, the price rose to a nine-week high during the week of December 8, almost reaching 152 cents a litre before falling slightly to 151 cents the following week.

"The real message to motorists is to plan when and where you're going to fill up to try to save as much money as possible," Mr Case said.

The RACV posts information about Victorian fuel price trends on its website.

Prices accurate at 4pm on Friday.