Average UK petrol prices are now at 131.60p a litre - down from 131.70p a week ago, but still above the 130.47p a litre average a month ago. Diesel forecourt prices have also fallen, from 136.37p last week to a mid-July average of 136.08p. A month ago, they were 135.70p.
The AA said: "UK average diesel pump prices, as reported last month, remain overblown.
"On paper, the wholesale price of diesel has been at or below the wholesale price of petrol since the beginning of July.
"Yet, diesel remains 4.5p more expensive at the pump - only slightly down from 5.25p in mid June."
AA president Edmund King added that the European Commission was pushing for greater openness in the pricing of fuel and even regulation to make it happen.
He went on: "After five years of surging pump prices, many UK drivers may actually welcome this bit of EU 'nannying' as a way to get a fair price at the pump."
At 136.6p a litre, Scotland's average price of diesel is the dearest in the UK, with Yorkshire and Humberside the cheapest at 135.7p.
Northern Ireland currently sells the most expensive petrol, averaging 132.4p a litre.