Ask anyone where the cheap fuel is and they'll say the supermarket. Ask them which supermarket and you'll start an argument. Asda people swear by Asda. Tesco people have their Clubcard. Someone always mentions Morrisons.
So we checked. We log every price change from every forecourt that reports to the Government's Fuel Finder scheme, which includes around 1,570 Asda, Tesco, Sainsbury's and Morrisons stations. Here's what eight months of that data says.
The short answer
Supermarkets really are cheaper than everyone else. Every month, for both petrol and diesel, without exception.
But which supermarket? That's where it gets a bit anticlimactic. Right now the big four are separated by half a penny on petrol. Sainsbury's is cheapest by a nose. Next month it could easily be someone else.
Supermarkets versus everyone else
This is the bit that's worth real money. Right now, on average:
| Fuel | Supermarkets | Other forecourts | You save |
|---|---|---|---|
| Petrol | 172.5p | 175.2p | 2.7p a litre |
| Diesel | 197.3p | 200.5p | 3.2p a litre |
| Super unleaded | 186.0p | 193.8p | 7.8p a litre |
"Other forecourts" here means every non-supermarket station that isn't on a motorway. We left motorway services out because they'd make the comparison look even more dramatic than it is.
On a 50-litre tank of petrol that's £1.35. On diesel it's £1.60. Not life-changing on one fill, but it adds up to £70 or £80 a year if you fill up weekly, and you don't have to do anything clever to get it.
And it holds every month. Here's petrol at the end of each month since February:
| End of | Supermarkets | Other forecourts | Gap |
|---|---|---|---|
| March | 151.4p | 154.4p | 3.0p |
| April | 154.5p | 157.6p | 3.1p |
| May | 156.7p | 160.0p | 3.3p |
| June | 149.0p | 151.7p | 2.7p |
| July | 157.9p | 160.9p | 3.0p |
| August | 159.0p | 162.5p | 3.5p |
| September | 172.4p | 175.1p | 2.7p |
Prices went up and down a lot over that time. The gap barely moved. Somewhere around 3p a litre, month in, month out.
So which supermarket is cheapest?
Here's petrol at each of the big four right now:
| Supermarket | Petrol | Stations |
|---|---|---|
| Sainsbury's | 172.8p | 315 |
| Asda | 173.0p | 404 |
| Tesco | 173.3p | 513 |
| Morrisons | 173.3p | 341 |
The gap between cheapest and dearest is half a penny. On a 50-litre tank that's 25p.
Diesel is the same story. Sainsbury's leads at 196.9p, then Asda at 197.5p, Tesco at 197.6p and Morrisons at 198.7p. A bit more spread, but still under 2p from top to bottom.
And the order doesn't stay put. Looking back over the months, each of the four has been cheapest for petrol at some point. Sainsbury's led in March, Morrisons in April and June, Asda in May, and Tesco in July, August and September. Nobody owns the top spot for long. They watch each other closely, and when one moves the rest follow within days.
Where it does matter: super unleaded
There's one exception worth knowing about. If you buy super unleaded, the supermarkets are not all the same.
| Supermarket | Super unleaded |
|---|---|
| Tesco | 183.9p |
| Sainsbury's | 184.9p |
| Asda | 190.5p |
| Morrisons | 190.8p |
That's a 7p a litre gap between Tesco and Morrisons, or £3.50 a tank. If you run a car that wants the good stuff, Tesco and Sainsbury's are the ones to aim for.
Bear in mind Asda only sells super unleaded at about 75 of its stations, so in plenty of places it isn't an option anyway.
What this means for you
Pick whichever supermarket is nearest. Seriously. The difference between them is smaller than the fuel you'd burn driving past one to get to another.
What does matter is choosing a supermarket over the branded forecourt next to it, which is worth around 3p a litre every time. And within any town, prices at individual stations can vary by far more than the brand average suggests. A particular Tesco might be 5p cheaper than the Tesco across town, because local competition matters more than the logo.
So the best habit is simple: check what's cheapest near you before you set off. Our town pages list every station within ten miles, cheapest first.
How we did this: averages are simple means across each chain's stations with a price reported in the last 30 days, matched by the brand name each station reports to the Fuel Finder scheme. Monthly figures are reconstructed from every logged price change. Obvious typos in the feed, prices far outside the normal range, are excluded. You're welcome to quote any of these figures; a link back is all we ask.