Biodiesel Fuel Prices and Operating Cost: What to Compare Before You Buy

What the Blend Labels Mean

Biodiesel is usually sold blended with petroleum diesel. The number after the B is the percentage of biodiesel in the fuel. Comparing prices only makes sense when you compare the same blend level.

B5 and below: In the US, diesel containing up to 5 percent biodiesel can be sold as ordinary diesel under the ASTM D975 specification, so you may already be buying it without a separate label. B6 to B20: Covered by the ASTM D7467 specification. B20 is the most common labeled blend and the one many diesel vehicle manufacturers address directly. B100: Pure biodiesel, which must meet ASTM D6751 before blending. It is less widely sold at retail and is approved by far fewer manufacturers for direct use.

Why Biodiesel Fuel Cost Moves Around

Biodiesel fuel cost is driven by different factors than petroleum diesel, which is why the gap between them changes over time rather than staying steady.

Feedstock prices: Biodiesel is made from vegetable oils, animal fats and used cooking oil. When those commodities rise or fall, the cost of producing biodiesel follows. Incentives and credits: Federal and state tax credits, renewable fuel requirements and state low-carbon fuel programs affect what blenders and retailers can charge. These programs have changed several times, so a price relationship you saw in past years may not hold now. Regional supply: Prices tend to be more favorable near production plants and in states with blending requirements or incentives. In areas with few suppliers, blends may be scarce or carry a premium. Petroleum diesel prices: Because most biodiesel is sold as a blend, the larger petroleum share means the blend's pump price largely tracks regular diesel. Season: Cold-weather blends and additives can affect availability and pricing in winter.

Pump Price vs. Cost per Mile

Biodiesel contains somewhat less energy per gallon than petroleum diesel. At low blends the effect on fuel economy is small and often hard to notice in normal driving. With B100 the drop is more noticeable. A blend that costs a few cents less per gallon can therefore end up roughly even with regular diesel on a per-mile basis, especially at higher blend levels.

The fairest comparison is cost per mile using your own fill-up records. Track several tanks on each fuel under similar driving conditions, because one tank is too noisy to rely on.

Cost per mile = price per gallon ÷ miles per gallon; Compare: regular diesel price ÷ your mpg on regular diesel; blend price ÷ your mpg on the blend

Ownership Costs Beyond the Pump

Cost factor | What happens | How it affects operating cost; Fuel filter | Biodiesel acts as a mild solvent and can loosen deposits left in the tank and lines by petroleum diesel | Expect an early filter change after first switching to a higher blend; afterward, intervals usually return to normal; Cold weather | Biodiesel begins to cloud and gel at higher temperatures than petroleum diesel, more so at high blends | Winter blends, additives or switching to a lower blend may be needed; a gelled filter means downtime; Seals and hoses | Some older rubber fuel-system components can degrade with high blends | Mostly a concern for older vehicles; a leak check after switching is sensible; Storage | Biodiesel is more prone to water absorption and degradation in long storage | Matters for seasonal equipment or vehicles that sit for months; Warranty | Each manufacturer sets a maximum approved blend | Using a higher blend than approved can complicate fuel-related warranty claims

How Engine Configuration Changes the Picture

Modern high-pressure common-rail diesels operate at very high fuel pressure and rely on precise injector tolerances. Off-spec or degraded fuel, whether biodiesel or petroleum, can contribute to injector and high-pressure fuel pump problems, which are among the most expensive repairs on a diesel. This is why fuel quality matters more than the label: buying from retailers that sell fuel meeting the applicable ASTM specification reduces risk.

Many newer diesels also use a diesel particulate filter that is cleaned through regeneration, sometimes using late fuel injection. In some engines, high biodiesel blends can increase fuel dilution of the engine oil during this process, which may justify closer attention to oil level and condition. This is one reason manufacturers limit approved blends on certain engines, so the approved level can differ between model years and powertrains of the same model.

What to Check Before Buying Biodiesel

Your vehicle's approved blend: Look in the owner's manual or near the fuel filler for the maximum biodiesel blend for your specific model year and engine. Approvals vary by powertrain, not just by brand. The blend at the pump: Compare like with like. A B20 price is not directly comparable to a regular diesel price that may already include up to B5. Fuel quality: Prefer stations whose fuel meets the relevant ASTM specification for the blend sold. Your climate: In cold regions, confirm whether winter blends are offered and whether you need additives. Your usage pattern: Vehicles driven regularly suit biodiesel blends better than ones that sit for long periods. A spare fuel filter: If you are switching to B20 or higher for the first time, budget for an early filter change.

Bottom Line

Whether biodiesel saves you money depends on local prices at the time you buy, the blend level, and whether your vehicle is approved for it. For an approved vehicle on B5 or B20, expect operating cost close to regular diesel, with the main extras being an early filter change and some winter planning. If the local price is favorable, it can be a sensible choice. If you are considering B100 or a blend above your manufacturer's approval, the potential repair and warranty risks usually outweigh small savings at the pump.