Drivers have been warned not to assume that the supermarkets are always cheapest for petrol and diesel.
Motoring organisation the RAC has called out the "Big Four" grocers - Tesco, Asda, Sainsbury's and Morrisons - for not cutting fuel prices quick enough.
The RAC said last week that wholesale price of petrol was back down to the levels recorded in early May of 131.75p per litre.
At this time, average unleaded prices were around 167p per litre - but right now, the average price is 178.93p per litre.
Last week, when the RAC issued its warning, the average price of unleaded was almost 183p.
How much has the price of petrol risen or fallen where you live? Let us know: mirror.money.saving@mirror.co.uk
The wholesale cost of petrol has fallen by 20p since early June, the RAC said - in comparison, UK retailers only dropped their pump prices by an average of 9p during July.
The RAC believes the biggest retailers’ failure to reduce petrol pump prices in line with the drop in the wholesale price of unleaded has cost drivers almost £9 more to fill up.
Drivers are being urged to compare prices of fuel to make sure they're getting the most for the money.
RAC fuel spokesman Simon Williams said "it's highly likely you'll find an independent retailer which is doing the right thing and fairly reflecting their lower wholesale costs by charging a lower price".
He said: "This is really encouraging because the independents buy new stock less frequently than the supermarkets as they don't sell as much, and consequently aren't as well positioned as their rivals to be able to snap up fuel at lower prices when there are sudden market drops."
Mr Williams continued: "We saw independent retailers leading the charge with fairer pump prices appearing all around the country which eventually forced the supermarkets to finally implement a more substantial cut late last Friday afternoon.
"What ought to have happened is that the biggest retailers cut their prices more significantly on a daily basis, given the wholesale price of petrol has fallen steadily over the last eight weeks."
Tesco has cut the price of petrol by 6.5p and diesel by 4.5p per litre, while Asda has slashed prices by 5p for petrol and 3p for diesel.
Sainsbury's has reduced fuel prices by an average of 5p, and rival Morrisons has cut prices by an average of 6p.
It comes after fuel prices hit their highest-ever levels earlier this summer as the cost of crude oil soared.
At their worst, prices reached 191.53p for petrol and 199.07p for diesel.
