Fuel prices in the UK have never been straightforward. Over the past few years, drivers have seen prices swing from record highs above 190p per litre to relative lows below 130p — sometimes within the span of a few months. Understanding what drives these changes can help you make smarter decisions about when and where to fill up.
Every litre of fuel you buy is a combination of four cost components. Knowing the split helps explain why prices move the way they do — and why they rarely drop as fast as they rise.
The wholesale cost of crude oil is the single biggest factor in pump prices. UK refineries buy oil priced in US dollars on international markets. When Brent crude rises from $70 to $90 per barrel, the wholesale cost of a litre of petrol increases by roughly 5-6p before tax.
Fuel duty is a flat tax of 52.95p on every litre of petrol and diesel sold in the UK. It does not change with the price of oil — whether crude is $50 or $150 a barrel, fuel duty stays the same. This means tax makes up a larger percentage of the pump price when oil is cheap, and a smaller share when oil is expensive.
VAT is charged at 20% on the total price including fuel duty. This means the government effectively taxes the tax — a detail that has frustrated drivers and campaigners for decades. On a litre priced at 140p, VAT adds roughly 23.3p.
The retailer margin covers transport, storage, staffing, and profit. Supermarkets typically operate on thinner margins (3-7p) to drive footfall, while motorway services and rural independents may charge 10-15p or more. This is where comparing prices on Tanki makes the biggest difference.
OPEC+ production decisions remain the most influential force on global oil prices. When the cartel cuts output, reduced supply pushes crude higher. Geopolitical events — conflicts in oil-producing regions, sanctions, or trade disputes — can cause sudden spikes that feed through to UK pumps within one to two weeks.
The GBP/USD exchange rate is the hidden factor many drivers overlook. Because oil is traded in US dollars, a weaker pound means UK refiners pay more for the same barrel of crude. A 10% drop in sterling against the dollar can add 3-4p per litre at the pump, even if oil prices haven't moved at all. Brexit-related currency shifts in previous years demonstrated this effect clearly.
Fuel prices follow recognisable seasonal patterns, though they can be disrupted by geopolitical events in any given year.
Spring and summer typically see prices rise. The "summer driving season" increases demand as families take road trips and holiday travel peaks. Refineries also switch to summer-grade fuel blends, which cost slightly more to produce. Prices tend to peak between May and August.
Autumn and winter often bring lower petrol prices as driving demand eases. However, diesel can remain elevated due to increased heating oil demand — diesel and heating oil are refined from the same feedstock. Cold snaps can tighten diesel supply further. January and February have historically been among the cheapest months to buy unleaded petrol.
This is one of the most common questions drivers ask, and the answer is nuanced. Analysis of UK station data shows that prices tend to be marginally lower on Mondays and Tuesdays, with slight increases towards the weekend when demand picks up. The difference is typically small — 0.5 to 1.5p per litre — but it adds up over a year of weekly fill-ups.
Supermarkets are more likely to cut prices early in the week to attract midweek shoppers, then hold or raise prices heading into the busier weekend period. That said, the variation between stations on any given day is far larger than the day-of-week effect. Checking live prices on Tanki will always beat guessing based on the calendar.
Tesco, Sainsbury's, Asda, and Morrisons collectively account for around 45% of UK fuel sales. Their pricing behaviour has an outsized effect on the market.
Loss-leader pricing is the key tactic. Supermarkets often sell fuel at or near cost to get customers into their stores, where the real profit is made on groceries. This is why supermarket fuel is consistently 3-8p per litre cheaper than branded stations in the same area.
Competitive clustering matters too. In areas where multiple supermarkets have nearby filling stations, prices are driven lower as they undercut each other. Conversely, in towns with only one supermarket filling station, that station may price closer to the local average. The most competitive pricing is typically found in urban areas with high station density — exactly the kind of pattern that shows up when you search for cheap petrol or diesel prices on Tanki.
You don't need to become an oil market analyst to save money on fuel. A few practical habits make a real difference:
Check before you fill — Prices can vary by 10-15p per litre between stations just a few miles apart. Use Tanki to compare live prices nearby before pulling into the first station you see.
Fill up early in the week — If you have flexibility, Monday or Tuesday fills tend to be slightly cheaper. Avoid filling up on Friday evenings when demand and prices are at their weekly peak.
Don't wait until empty — Filling up when you still have a quarter tank gives you the flexibility to wait for a better price or detour to a cheaper station. Running on fumes forces you into whatever station is closest, regardless of price.
Watch for wholesale drops — When oil prices fall sharply, wholesale fuel costs follow within days, but pump prices can take one to two weeks to adjust. Stations in competitive areas tend to pass on savings faster. If you see oil prices dropping in the news, it may be worth waiting a few days before filling up.
Tax accounts for over half the pump price, and you can't control oil markets or exchange rates. What you can control is where you fill up and how you time it. The single most effective thing any driver can do is compare prices before every fill-up. Even saving 5p per litre on a 50-litre tank adds up to over £130 per year.
Compare live fuel prices from over 7,500 UK stations
Find Cheap Fuel on Tanki →Related reading: 15 ways to save money on fuel · E10 vs E5 petrol explained · Best fuel cards UK