Petrol prices are jumping just in time for Christmas.

The difference between the wholesale and bowser price of petrol is at a record 15 cents a litre, with retailers accused of opportunistic price gouging.

Australians paid an average $1.23 a litre at the pump last week, with some retailers pushing the price as high as 134.9 cents a litre at a time when it costs them just $1.07 a litre wholesale.

Gasoline prices in Singapore, where most Australian fuel is imported from, have fallen by about 15 cents a litre since early October, but Australian wholesale prices are only down 12 cents, while the average price at the bowser is less than 10 cents lower.

CommSec’s chief economist Craig James told the ABC that petrol stations’ profit margins were at record highs, and that drivers should shop around.

“The smooth margin — and we’ve looked at the five-week average — stood at a record 15.1 cents a litre,” Mr James told ABC News.

“It does pay you to shop around the place, use some of the apps which are available now to be able to record where the cheapest price is, and hopefully that puts pressure on the petrol marketing groups to reduce their prices a bit.”

The difference between the highest and lowest petrol prices for regular unleaded can be as high as 34 cents a litre in Melbourne, and 23 cents a litre in Sydney.

The good news, Mr James said, was that the petrol price remained cheaper than it was 12 months ago and was tipped to go lower.

But that’s no consolation to families struggling to fill their tanks this Christmas.

An analysis by The Australian found that, in many cases, it was cheaper to fly than to hit the roads this silly season.

Comparing the prices of discount airfares for a young family of four on popular domestic routes, the newspaper found that flying was cheaper or on par, depending on the model of car driven and whether luggage was checked in.

The average price across capital cities yesterday was $1.17 a litre in Sydney, $1.19 in Adelaide, $1.19 in Melbourne, $1.31 in Perth and $1.27 in Brisbane.

Almost half of 500 outlets in metropolitan Melbourne monitored by the RACV lifted prices by about 25c a litre to $1.12 a litre on Monday, following dozens that moved earlier. Most were expected to jump by Christmas Day.

Dozens of Melbourne petrol stations raised their prices to a peak of a 134.9c a litre.

RACV vehicle engineering acting manager Nick Platt slammed the “completely unjustified” tactic given a relatively low wholesale price in recent weeks.

Mr Platt urged motorists to give “inflated” bowsers a wide berth, and to fill up now at cheaper outlets before they too raised prices.

“There isn’t any legitimate reason for petrol or diesel prices to increase over the Christmas

period. If anything they should continue to fall to reflect lower oil prices,” Mr Platt said.

The peak price was about two cents a litre higher than warranted based on usual price cycle patterns, he believed.

The industry has denied price gouging, saying the increase and timing is part of the usual fluctuating price cycle.

Angry motorists have complained of weak regulation allowing “rip offs”.

But Mr Platt said the Australian Competition and Consumer Commission could not control prices in a free market.

“At the end of the day ... it is up to consumers to shop around,” he said.

The ACCC said: “Wholesale and retail petrol prices in Australia are not regulated. Fuel prices are set by participants in the relevant market”.

Its petrol monitoring report last year found there was “little evidence to support the claim that price cycle increases before public holidays are always higher than the price cycle increases when there is no public holiday”.

Australian Retailers Association executive director Russell Zimmerman said the timing was unfortunate.

“It is obviously disappointing to see petrol prices rising at the moment when it is already a very high spend at Christmas time for household budgets,” Mr Zimmerman said.

Melbourne’s average unleaded price yesterday of 112.3c a litre remained the cheapest of the nation’s capital cities, according to Motormouth data.

Australasian Convenience and Petroleum Marketers Association CEO Mark McKenzie denied price gouging.

“This is part of a normal price cycle that has coincided with the Christmas break. Past research has found prices go up about half the time in advance of holidays,” he said.

CommSec chief economist Craig James said the national unleaded average price of 123.9c a litre in the last week was at a 10-month low, and still lower than Christmas last year.

NRMA spokesman Peter Khoury told The Australian the Sydney average would likely fall by six to seven cents a litre, with hopes that some petrol stations may drop the price of unleaded as low as $1 a litre.