Fuel prices dropped for the second consecutive month in June, but both diesel and petrol prices remain higher than the RAC believes they should be.
Petrol prices dropped by 3p to 145p a litre last month, while diesel fell by close to 4p to under 150p, but the automotive service group claimed it was "still too expensive" when compared against wholesale prices.
Shell ranked top for the highest fuel prices across its 535 sites, with its petrol prices close to 4p more than the UK average at 149p per litre and its diesel 5p ahead of the norm.
Meanwhile, BP was close behind in second with an average of 146.5p per litre of petrol and 152p per litre of diesel.
RAC's Simon Williams said: “While it’s good news prices at the pumps have fallen for the second month in a row, this also leaves a bad taste in the mouth because we know drivers in Great Britain are continuing to get a raw deal.
"We remain baffled how the very same fuel can be sold for such vastly different prices by the biggest retailers, whether they’re run by supermarkets or the world’s largest oil companies.
“We will continue to highlight this disparity, along with the massive differences between major retailers’ high and low prices, to the new government and the Competition and Markets Authority with a view to them being addressed."