What is being claimed
The advice doing the rounds since the weekend is that pump prices rise as the weekend approaches, so drivers should refuel before Thursday 17 September. The reasoning offered is that retailers lift prices ahead of weekend leisure traffic, and the saving quoted is usually two or three pence a litre.
The trouble is the cut-off keeps moving. Some outlets say before Thursday. Some say before 5pm on Thursday. Some say before 10am on Thursday, on the basis that forecourts reprice in the late morning once the markets have opened. Those cannot all be true, and none of them comes with a dataset attached. What sits behind them is commentary from motoring and car-buying sites, not published price records.
Two or three pence, at the very best: Take the claim at face value and assume the effect is real and worth 3p a litre. On a 55-litre tank that is £1.65. Choosing a different forecourt in the same region is worth tens of pounds on the same fill. The day-of-week advice is not wrong so much as it is aimed at the wrong variable — it optimises the smallest number in the equation.
The number that actually decides what you pay
As of 09:42 this morning, our live tracker put the UK average at 170.5p for petrol and 192.9p for diesel across 8,047 forecourts. Underneath those averages sit the figures the national coverage never mentions:
- Cheapest petrol in Britain: 142.9p a litre, at Ravenspoint Trading Ltd in HS2 9QA.
- Most expensive petrol: 239.9p a litre, at an independent forecourt in BS35 4JB.
- That is a spread of 97.0p a litre, or £53.35 on a 55-litre tank of the same fuel on the same morning.
- On diesel the spread is 84.0p — 146.0p at Burra Motor Repairs in ZE2 9LB against 230.0p in CA10 1BL. That is £46.20 a tank.
Those extremes are remote and motorway sites, and nobody is driving from Bristol to the Outer Hebrides to save fifty pounds. But the same pattern repeats at every scale. Within a single town it is routinely 10p a litre or more between forecourts a few miles apart, which is over five pounds a tank — three times what the Thursday advice offers even if the Thursday advice is right.
Why the spread is so wide at the moment: In a fast-rising market, some retailers reprice within a day of a wholesale move and others take a fortnight. The slow ones are briefly the cheap ones, which is exactly why the gap between forecourts widens when prices climb. It also means the ranking changes week to week, so the forecourt that was cheapest near you last month is not necessarily cheapest now.
Meanwhile, diesel has gone through its 52-week high
This is the part of the week that actually deserved the headlines. The official weekly figures published yesterday put petrol at 168.14p and diesel at 190.72p, up 3.74p and 4.36p in seven days. Petrol is now exactly level with its 52-week high. Diesel's 52-week high was 192.14p, set in April — and our live average this morning is 192.9p, which puts diesel above the April peak and at its highest since 2022.
Over twelve weeks petrol has risen 17.12p, or 11.3%, and diesel 23.60p, or 14.1%. A 55-litre diesel fill now costs around £106 against roughly £94 for petrol. The diesel premium is 22.4p a litre, which is the widest of this entire crisis.
We set out the oil-market side of this last week when Brent first cleared $100, in petrol hits a new crisis high as diesel closes in on April's peak. Brent has kept going since, trading around $108. But crude is no longer the whole story on diesel.
Why diesel and not petrol
The squeeze has moved from the barrel to the refinery. Diesel and the other middle distillates are the scarce part of the barrel right now, and the evidence is in the refining margins rather than in crude:
- US retail diesel passed $6 a gallon on 11 September, the first time on record, with crude well below where it traded at the 2022 record.
- The US diesel crack spread — the margin between diesel and crude — hit a record of roughly $108 a barrel at the start of the month.
- Distillate stocks are running around 13% below the five-year average as the heating season starts.
- Roughly a quarter of Russian refining capacity is offline, and Saudi Arabia's Jazan refinery was struck again on 7 September.
- Refiners tilted their yields toward jet fuel when aviation margins led, which thinned diesel output just as harvest and heating demand arrived.
Heating oil is chemically almost the same product as diesel, which is why rural households are seeing it too: prices have gone from around 60p a litre to close to 97p, with the worst of it landing on homes off the gas grid.
The practical implication matters more than the mechanism. If crude eases back, petrol should follow fairly promptly. Diesel need not, because its problem is refining capacity rather than the price of oil. That is the honest answer to the £2-a-litre diesel headlines circulating since last week: it is possible, it would need this refining squeeze to persist through winter, and it is not a forecast anyone should be treating as settled.
So is there a best day to buy fuel?
We are not going to tell you there is, because we cannot show you the figures — and neither can anyone else who is currently telling you Thursday at 5pm. What we can say from the data we do publish is that any day-of-week effect is small enough to be swamped by three other things: which forecourt you use, which brand it is, and whether your retailer has repriced yet this week.
There is also a timing point that cuts against the advice this week specifically. The usual logic of “wait for a better day” assumes a flat or falling market. In a rising one, waiting costs money. Wholesale increases from the start of September are still feeding through to forecourts, so the direction of travel between now and Thursday is up regardless of what day it is.
What to do instead of watching the calendar:
- Check the forecourts, not the day. Our live comparison and fuel map show what every station near you is charging, refreshed every 15 minutes from the Government's Fuel Finder feed.
- Fill sooner rather than later this week. With wholesale rises still working through, this is not a market to wait out.
- Avoid motorway services if you can plan ahead. They sit at the expensive end of our rankings almost every day, typically well above the local alternative a couple of junctions off.
- Save your regulars to Favourites so you can see which of your usual stations has repriced and which has not.
- Diesel drivers, compare harder. With a 22p premium and an 84p national spread, comparison is worth proportionally more to you than to petrol drivers.
- Long trip coming up? The journey planner finds the cheapest stops along your actual route rather than the nearest ones.
What to watch next
The next official weekly figures land on 22 September and will show whether the live average's move above 192p holds in the national series. The Budget on 28 October carries the fuel duty decision, with duty currently frozen at 52.95p a litre to the end of the year. And the question underneath everything is whether refining capacity recovers before winter demand peaks, because that, not crude, is what sets diesel now.
For trends, our price charts and UK Fuel Price Index track the official weekly averages as they publish. For what you will actually be charged this afternoon, use the live tracker. The second one is the one that saves you money.
Sources and dates: weekly UK average pump prices are the Department for Energy Security and Net Zero road fuel price statistics for the week ending 14 September 2026, as published on our UK Fuel Price Index. Live averages, spreads and named forecourts are from the UK Government Fuel Finder API as at 09:42 on Tuesday 15 September 2026, covering 8,047 forecourts, and will have moved since. Refining margins, distillate stocks, US diesel prices and heating oil figures are from market and news reporting in the week to 14 September 2026. Fuel duty is 52.95p a litre with VAT at 20% on top. Day-of-week refuelling claims described here are as published by third parties; we have not verified them and quote them only to set out what is being advised.