The AA has joined calls for retailers to pass on a fall in the wholesale price of petrol to motorists.
Pump prices have "barely budged" from the late summer high of just over 138p a litre despite a 2p-a-litre fall in the wholesale price of petrol a fortnight ago and a further 3p drop last week, according to the latest AA Fuel Price Report.
Petrol averaged 132p at the start of the year, "and this is where it should be heading if the wholesale price collapse persists", the report said.
On Tuesday, the average price of petrol across the UK stood at 137.64p a litre, despite Asda cutting its national petrol price cap to 133.7p last week and some independent retailers beginning to take a penny off the cost of a litre.
Throughout the July to mid-September holiday period UK drivers paid on average 1.5p a litre more than they did last summer, although the cost of petrol failed to repeat the brief 140p-a-litre surge this time last year.
A comparison of wholesale and pump figures showed the impact of turmoil in Egypt and Syria lifted prices to above 137p from late July, followed by a fall in wholesale prices a fortnight ago and a "collapse" in the past 10 days.
However, even last week pump prices continued to creep up, the report shows.
The average price of diesel in the UK has risen from 141.87p a litre in mid August to 142.50p in mid September.
The AA urged fuel retailers to pass on cost savings quickly, but said it was mindful of the volatility in the fuel price market.
It added that over the weekend, drivers in many towns across the UK were being charged at least £2.50 a tank more for supermarket petrol than in towns just down the road.
It has reacted by offering its longer-serving members a free fuel price locating smartphone tool to help them beat what it describes as "the UK's pump price postcode lottery".
Regionally, London remains the cheapest UK region for buying petrol at 137.1p a litre and Northern Ireland the most expensive at 138.6p. Wales, at 138.2p, is the only other region with petrol averaging above 138p a litre.
Predominantly rural Scotland (143.4p), Wales (143.1p) and Northern Ireland (143.0p) are the dearest for diesel compared with London which is the cheapest at 141.8p a litre.
AA president Edmund King said: "UK drivers have to accept that, with such huge volatility in the international oil and fuel markets, average pump prices aren't going to follow every twist and turn of the wholesale prices. Indeed, our track of unleaded petrol prices shows that the industry insulated drivers against some of the late July surge despite the retailers' attempt to talk up the price and scare away more of their customers.
"However, we draw the line at the blatantly unfair pump price postcode lottery. Yes, Asda's prices are exceptionally low, with some independent retailers undercutting even that. But, in other towns last weekend, putting a fuel nozzle against the head of many of our members and forcing them to pay 5p a litre more for the cheapest petrol was inexcusable."
Earlier this week the RAC urged fuel retailers to "immediately" ease pressure at the pumps by passing on a drop in wholesale prices.
It said a litre of unleaded petrol sold wholesale for 6p less since the end of August, while diesel was down by 2p a litre, giving petrol stations the power to lower prices on the forecourt.