Supermarket vs BP and Shell petrol prices: the 5p a litre gap

Supermarket forecourts remain the cheapest mainstream places to fill up in the UK, and the gap to the biggest oil-company brands is now about 5p a litre. FuelWise's figures for 21 October show Sainsbury's averaging 171.6p a litre for E10 unleaded, against 176.7p at both BP and Shell. That is a difference of about £2.80 on a 55-litre tank.

National prices barely moved this week. The UK average for E10 is 174.1p and for standard diesel 199.1p, each down 0.3p in seven days. With Brent crude still near five-month highs, where you buy matters more than when.

Supermarkets against the big brands

Across the 2,342 supermarket forecourts in FuelWise's data, E10 averages 171.6p and diesel 196.4p. Other non-motorway forecourts average 174.7p for E10 and 199.9p for diesel. That puts supermarkets about 3.1p a litre cheaper for petrol and 3.5p cheaper for diesel.

The four big supermarket chains sit within half a penny of each other:

• Sainsbury's: E10 171.6p, diesel 196.4p
• Morrisons: E10 171.7p, diesel 196.9p
• Asda: E10 171.9p, diesel 196.7p
• Tesco: E10 172.1p, diesel 196.7p

The difference is larger at the oil-company brands. BP and Shell both average 176.7p for E10 and 201.6p for diesel. Both brands' diesel averages are above £2 a litre, and so is Esso's, at 200.2p (E10 174.8p). Diesel at Sainsbury's is 5.2p a litre cheaper than at BP or Shell, which saves about £2.86 on 55 litres.

Not every branded forecourt is expensive. Texaco averages 172.6p for E10 and 197.9p for diesel, and Jet averages 172.8p and 198.2p. Both are within about a penny of the supermarkets for petrol. Brand averages hide a wide range between individual forecourts, so the brands page is worth checking for your local options.

Motorways: about 20p a litre more

Motorway service areas are still in a different league. Across 144 motorway forecourts, E10 averages 192.1p and diesel 215.7p. That is 20.5p a litre more than the supermarket average for petrol and 19.3p more for diesel. On a 55-litre tank, filling up on the motorway rather than at a supermarket costs about £11 more for either fuel. Filling up before a long journey is still one of the easiest savings a driver can make.

Northern Ireland well below the rest of the UK

The regional figures show one clear outlier. In Northern Ireland, E10 averages 166.3p and diesel 191.3p, both about 7.8p below the UK average. Prices there also fell faster this week, by 0.6p for both fuels. All five council areas with the cheapest unleaded in the UK are in Northern Ireland, led by Antrim and Newtownabbey and Causeway Coast and Glens, both at 165.5p. The two brands with the lowest averages, Maxol (E10 166.5p, diesel 190.7p) and Circle K (E10 167.0p, diesel 192.2p), are close to the Northern Ireland average.

In Great Britain the regional spread is narrow, at about 3.4p for E10. The North East is cheapest for petrol at 172.5p, followed by Yorkshire and the Humber at 172.9p. The South East is dearest at 175.9p for E10 and 200.6p for diesel. London (200.4p) and Scotland (200.5p) also average more than £2 a litre for diesel. Scotland had the largest weekly fall in E10 in Britain, down 0.7p to 174.9p.

The local spread is wider than the regional one. The dearest council area for unleaded is West Berkshire, at 182.2p, which is 16.7p above the cheapest areas in Northern Ireland. Tandridge (181.4p) and Uttlesford (181.1p) follow.

Why prices are stuck near record levels

FuelWise recorded 8,400 price changes in the past seven days. Of those, 5,986 were cuts and 2,414 were rises, so about seven in ten moves were downward. Even so, the national average fell by only 0.3p.

The main reason is the conflict in the Middle East. According to Reuters, Brent crude reached $111.99 a barrel on Tuesday 20 October, a five-month high, before settling at $108.79. Traders were weighing talks between Iran's president and Pakistan's army chief, whom Reuters describes as a key US-Iran mediator, against continued Houthi attacks on Saudi infrastructure. The Houthis said they had targeted sites including an Aramco facility at Yanbu and the Shaybah oilfield. Saudi authorities did not immediately confirm the claims. Shiptracker Kpler reported at least 18 vessels attacked over two weeks.

Early on Wednesday, Reuters reported that Brent had risen again to $109.64. It cited Iranian media reporting that a supertanker caught fire after hitting a sea mine south of the Strait of Hormuz. LSEG analysts said in the same report that attacks on tankers had spread beyond the strait to the Gulf of Oman.

Diesel costs about 25p a litre more than E10 at UK pumps, and diesel supply is a particular concern in world markets. Reuters reported that Russian diesel cargoes are returning to traditional destinations, including Turkey and Brazil, after the US suspended sanctions. It also reported that US energy officials are working with refiners to raise output because a diesel shortage has pushed up prices. None of the sources say when or by how much this might affect UK prices.

One thing has worked in drivers' favour. Oil is priced in dollars, so a stronger pound makes it slightly cheaper to import. Reuters' Trading Day column reported that sterling rose to a five-week high on Tuesday as the dollar weakened broadly.

What the regulator says about margins

The Competition and Markets Authority (CMA) is watching how quickly cost changes reach the pumps. In its August monitoring update, it said it had found no evidence that retailers had actively changed their pricing strategies to take advantage of the crisis. However, it said passive pricing by most retailers was contributing to sustained high margins. It also found that some retailers did not immediately pass on falls in wholesale diesel prices.

The CMA said an autumn review would examine whether wholesale changes reach retail prices on time and why prices vary between local areas. Chief executive Sarah Cardell said the CMA expects "any reductions in wholesale prices to be rapidly and fully passed on to drivers". The CMA also said about 97% of UK petrol stations are registered with Fuel Finder, accounting for an estimated 99% of fuel sold.

What this means for your next fill-up

• Check a supermarket first. On average, Sainsbury's, Morrisons, Asda and Tesco are 3p to 5p a litre cheaper than other forecourts and the big oil brands.
• Don't assume a brand is dear. Texaco and Jet average close to supermarket prices, but individual forecourts vary.
• Avoid motorway forecourts where you can. They average about 20p a litre more than supermarkets.
• Compare locally. In Britain, the gap between areas is much bigger than the gap between regions. The live price map shows every forecourt's latest price, and the diesel prices page tracks the national diesel average.

For the longer view, the weekly Price Pulse found that petrol fell 0.5p and diesel 0.7p in the week to 18 October.