The Office of Fair Trading (OFT) is investigating whether reductions in crude oil prices are being passed on to motorists.
It is claimed that when the cost of oil goes up, the price of petrol and diesel follows. But when oil costs falls, prices at the pumps takes longer to follow.
Campaigners have been pushing for parity on prices, particularly in the Scottish islands where drivers pay most. Earlier this year a petition calling for a probe into pricing by distributors in the Western Isles attracted more than 1600 signatures.
The average price for unleaded petrol on Lewis is 148.6p, compared to 138.8p in Renfrew-shire, 137.2p in Edinburgh and 136.8p in Plymouth.
Claire Hart, director in the OFT's services, infrastructure and public markets group, said: "We are aware of widespread concern about the pump price of petrol and diesel and we have heard different claims about how the market is operating."
Scottish Secretary Michael Moore, who had talks on the issue with the watchdog's chief yesterday, said: "Motorists are concerned about the prices they are having to pay at the pumps. It is good news the OFT will look into this and motoring groups and consumer bodies will have the chance to have their say."
The OFT said it will be gathering information over the next six weeks and plans to publish its findings in January.
Petrol prices rose by 38% between June 2007 and June 2012, while diesel prices went up by 43% over the same period. The UK retail road fuels sector is estimated to be worth around £32 billion, the OFT said.
Quentin Willson, former Top Gear presenter and FairFuelUK campaigner, said: "There is a widespread feeling that when oil goes up, pump prices rocket immediately – but when the oil price falls, pump prices don't reflect that fall. This causes exasperation and anger."
RAC Foundation director Professor Stephen Glaister said: "We have always argued for pricing transparency and this review promises to provide it. We also welcome scrutiny of what the decline in the number of petrol stations has meant for fuel supply and price.
"In 1990 there were some 18,000 forecourts. Now there are fewer than 9000."
SNP transport spokesman Angus MacNeil MP said: "I hope the whole chain is looked at, from the refinery to the fuel tank and all handlers in-between. We need a definitive view of what exactly creates the problem, particularly in rural areas."
The OFT is seeking information from the industry, motoring groups and consumer bodies. It will explore claims about how the road fuels sector is functioning, including whether supermarkets and oil companies are making it more difficult for independent retailers to compete.
The review will also consider whether there is a lack of competition between fuel retailers in remote communities.
The OFT began to look at the issue in February when it received a submission from the Retail Motor Industry (RMI), which raised concerns about the ability of independent fuel retailers to continue to compete.
A Department for Transport spokesman said: "We look forward with interest to the findings of the study."