What is B7 diesel?

What B7 actually means

The "B" stands for biodiesel and the number is the maximum percentage in the blend. B7 diesel is ordinary mineral diesel containing up to 7% fatty acid methyl ester (FAME), the biodiesel component, which is there to cut lifecycle carbon emissions.

These labels appeared on UK pump nozzles and vehicle filler flaps in 2019 under a Europe-wide fuel labelling standard — the same exercise that gave petrol its E5 and E10 labels. The fuel itself did not change when the stickers went up. If you have been buying "diesel" in the UK for the last decade, you have been buying B7.

You may also see B100 (pure biodiesel) or XTL (synthetic paraffinic diesel, including HVO) at a small number of sites. Neither is interchangeable with B7 unless your vehicle is specifically approved for it.

What diesel costs today

Across 1,485 forecourts publishing a diesel price, the UK average is 197.4p a litre, ranging from 107.9p at the cheapest site to 226.5p at the most expensive — a spread of 118.6p, or £65.23 on a 55-litre tank.

See how much diesel costs in the UK for the full breakdown by region and retailer, or find the cheapest diesel in your town.

Why diesel costs more than petrol

Fuel duty is currently levied at the same rate per litre on both petrol and diesel, so the difference at the pump comes from the wholesale side.

A barrel of crude yields a fixed slate of products, and European refineries are configured to produce proportionally more petrol than the continent's vehicle fleet actually consumes — the fleet skews diesel, especially in commercial transport. The shortfall is made up with imports, which carry shipping and handling costs that petrol, often in surplus and exported, does not.

Diesel demand is also tied to freight and agriculture rather than leisure driving, so it holds up through the winter when petrol demand softens. That keeps diesel's wholesale price comparatively firm in exactly the months when petrol gets cheaper.

Is premium diesel worth it?

Premium diesel — sold under names like V-Power, Ultimate and Momentum — is the same B7 base fuel with a heavier additive package: detergents to keep injectors and the combustion chamber clean, sometimes a cetane improver, sometimes a lubricity additive.

It costs meaningfully more per litre. For a well-maintained modern car doing ordinary mileage, the evidence for a return on that premium is thin, and standard B7 from a busy forecourt with high turnover is a sound choice. The case is stronger for high-mileage vehicles, engines with a known injector fouling issue, or a car that has run a long time on cheap fuel — an occasional tank of premium as a clean-up is a reasonable idea.

As with petrol, the size of that premium is almost always smaller than the gap between the cheapest and most expensive forecourt within a few miles of you. Finding the right station matters more than choosing the right grade.