ACCC research has found that between the beginning of July 2014 and early January 2015, the average wholesale price of regular unleaded petrol in Australia's five largest cities decreased by around 35 cpl.

Over the same period, average retail petrol prices in the cities decreased by around 38 cpl.

In July 2014 the monthly average retail price of petrol across regional locations in Australia was 5.7 cpl higher than prices in the five largest cities. By December 2014 that difference had blown out to 17.6 cpl.

"Motorists in our larger capital cities have therefore seen the benefit of lower international prices, but consumers in a number of regional locations have not," ACCC chairman Rod Sims said.

"While lags are expected, as older stocks can take longer to run down in regional locations, we would expect the falls to be passed on reasonably quickly."

Speaking to the Stawell Times-News within hours of the release of the ACCC's comprehensive research, Mr Sims said there has been a lot of concern about the slowness of price reductions in regional and rural areas.

"It doesn't look like prices have fallen as they should have," he said.

"The international price of petrol has fallen 35 cents over the last six months. There is really no reason why prices in regional and rural areas shouldn't have come down by that much now either.

"If there hasn't been that drop in the price of fuel, retailers need to be able to demonstrate and have a good explanation as to why."

Mr Sims has urged the region's motorists to do the math and exercise common sense when filling up at the bowser.

"Consumers need to think back to six months ago and ask themselves - What was I paying then?" he said.

"Now there has been a 35 cent decrease in the international price of petrol since and if they haven't experienced that they should be asking retailers - Why hasn't the price come down?"

Despite the price of US crude oil crashing to below $50 a barrel, more than half of what it was six months ago, the region's motorists have continued to pay around $1.20 a litre for fuel while their city counterparts enjoy prices at 99 cpl.

Mr Sims has also provided details on the ACCC's new approach to monitoring and analysing fuel markets, which will be in a more regular and in-depth way.

This year, the ACCC will produce quarterly reports looking at petrol price movements and what drives them overall.

The quarterly reports will cover fuel price movements in all capital cities and around 180 regional locations and will examine issues including the drivers of petrol prices (i.e. international refined petrol prices, terminal gate prices and the AUD-USD exchange rate).

"These quarterly reports could, for example, focus on the lags between international refined petrol price movements and changes in retail petrol prices in both the larger capital cities and in regional locations," Mr Sims said.

There will also be at least four market studies looking at 'micro' issues in considerable depth, including analysing the price drivers of petrol in three regional markets.

Mr Sims said the ACCC will look at three regional locations closely this year to understand their level of petrol prices in more detail.

"The studies will look at the cost of fuel in the nearest port, transport and storage costs, as well as wholesale, distribution, and retail costs to fully explain prices and where money is being made in the petrol price value chain," he said.

"We will only name the regional locations to be studied in this way once the compulsory notices have been issued. Otherwise, we run the risk that market behaviours change before our study begins.

"We expect to identify the three regional locations to be studied in the coming months, with the first to be announced in March. The reports will be delivered progressively throughout the year."

Mr Sims said the ACCC understands that many regional communities want to be the first target of the market studies, however given the in-depth nature of the studies only three can be done in any year.

"After the three market studies into particular regional areas we will be able to draw lessons of wider relevance to other regional markets," he said.

"We may find consumers and local authorities in regional areas will have a better ability to understand what drives their fuel prices."

Mr Sims emphasised that petrol prices are not regulated in Australia, and retailers are free to set petrol prices at levels that see them competitive in the market.

"This highlights the importance of the ACCC's new petrol market studies," he said.