Major retailers including the "Big Four" supermarkets have been criticised for failing to cut petrol prices in line with falling wholesale costs.
Tesco, Asda, Morrisons and Sainsbury's all reduced their fuel prices in the last week - but motoring group the RAC claims the cuts are not enough.
RAC figures show the wholesale price of petrol is back down to the levels recorded in early May of 131.75p per litre.
At the time, average unleaded prices were around 167p per litre - but right now, the average price is 182.11p per litre.
UK retailers only dropped their pump prices by an average of 9p during July, the firm said.
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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.
The wholesale cost of petrol has fallen by 20p since early June, according to the RAC.
RAC fuel spokesman Simon Williams said: "July has been an unnecessarily tough month for drivers due to the big four supermarkets' unwillingness to cut their prices to a more reasonable level, reflecting the consistent and significant reductions in the wholesale cost of petrol and diesel.
"As it was, 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."
The RAC said drivers filling up at the end of July average of 183p per litre could be paying almost £9 a tank more than they should be.
Motorists should now be paying about 182p per litre for diesel, the motoring firm claimed - nearly £6 a tank lower than the end of July average of 192p per litre.
Mr Williams advised drivers that they should no longer assume supermarkets are the cheapest places to get fuel.
He said motorists should "shop around as 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 added: "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."
Tesco has cut the price of petrol by 6.5p and diesel by 4.5p, while Asda has slashed prices by 5p for petrol and 3p for diesel.
Sainsbury's has reduced fuel prices by an average of 5p. Morrisons has cut prices too but hasn't revealed how much by.
A spokesperson for Sainsbury's said: "We are committed to offering motorists great value and over the weekend we lowered the price of petrol and diesel across our forecourts.
"We price locally and competitively."
The Mirror has contacted Tesco, Asda and Morrisons for comment.
