Drivers face mixed fortunes as diesel falls but petrol rises in May

May proved to be a month of two very different fortunes for drivers, with the average price of a litre of petrol going up nearly 2.5p and diesel coming down 4.5p, analysis of RAC Fuel Watch data reveals.*

The average price of a litre of unleaded rose from 157p to 159.4p (2.4p) whereas diesel fell from 188.4p to 183.9p. The petrol increase cost drivers an extra £1.32 every time they filled up a typical 55-litre family car (£86.36 to £87.68) and the drop in the cost of diesel saved drivers £2.50 a tank (£103.68 to £101.13).

The price differences were caused by the wholesale cost of petrol rising mid-month while the diesel equivalent reduced, closing the gap between their wholesale prices to just 10p at one point. On 14 May a litre of delivered petrol cost retailers 123.5p – before retailer margin and VAT – while the diesel equivalent was 133.3p. Despite this, the gap between pump prices for the two fuels is currently 25p.

Buying petrol at one of the big four supermarkets worked out to be 4p a litre cheaper in May as the average price was 155.6p at the end of month, compared to the UK average of 159.4p. Supermarket unleaded only went up 1.4p in contrast to the UK average increase of 2.4p. Supermarket diesel, however, was only 1.4p less than the UK average at 182.5p on 31 May, having come down 4p (3.9p) in the month.

RAC head of policy Simon Williams said: “May was a better month for drivers of diesel vehicles than it was for petrol. Those relying on unleaded had to endure yet another rise at the pumps, while those who use diesel saw a welcome 4.5p reduction. 

“It’s really quite unusual to see the price of one fuel go up and the other come down. This was brought about by the wholesale cost of unleaded rising due to higher demand in the United States. This coincided with a drop in demand for heating oil in western Europe which is refined from the same part of the barrel as diesel. 

“The last week of the month also saw the price of Brent crude drop below $100 which ought to prove to be good news for drivers as it should lead to far lower prices. The wholesale price of diesel has been far lower than its peak for some time which we had hoped would yield far bigger forecourt reductions. Petrol, however, could have risen further than it did, so it might have been the case that retailers decided to keep the price of unleaded down at the expense of greater diesel reductions.

“On 1 June the Competition and Markets Authority published its latest report on the road fuel market which found retailers hadn’t altered their pricing strategies during the war but these were largely passive and lacking in competition. It also said that retailer margins remained at historically high levels and that it would be concerned if current high retail prices persist given wholesale prices are no longer increasing.

“We hope its next report shows that drivers have been treated fairly by retailers reducing their pump prices in line with the fall in wholesale costs.”

Drivers looking to save money on their fill-ups should take advantage of the fuel finder feature in the free myRAC app. The app can be downloaded from the App Store or Google Play, and drivers don’t need to be RAC members to use it. Up to 10 searches a day can be made over a two, five or 10-mile radius, with each giving the five cheapest prices. 

The RAC Fuel Watch web page has more information about the average price of petrol and diesel at the big four supermarkets and at motorway services. It also features graphs showing average prices since 2000 as well as a daily financial breakdown of the cost of a litre of petrol and diesel.

^{* UK average pump prices quoted are based on the Government Fuel Finder data from 1-31 May 2026. Wholesale prices are from the Oil Market Journal 1-29 May.}