Biodiesel vs Biofuel: Understanding the Difference

The Short Answer

Biofuel is the broad category. Biodiesel is one specific member of it. Any fuel made from recently living biological material, such as vegetable oils, animal fats, crops, crop waste or used cooking oil, counts as a biofuel. Biodiesel is a particular biofuel made from oils and fats and designed to replace or blend with petroleum diesel in compression-ignition (diesel) engines.

One qualification matters for drivers. Because "biofuel" covers fuels for very different engines, the two terms are not interchangeable at the pump. Ethanol is also a biofuel, but it belongs in gasoline engines. Biodiesel belongs in diesel engines. Putting the wrong biofuel in the wrong engine can cause serious problems, so the useful question is not whether a fuel is a biofuel but which biofuel it is and whether your engine is approved for it.

What Counts as a Biofuel

The term describes where a fuel comes from, not how it behaves in an engine. Biofuels can be liquid or gaseous and can be made by fermentation, chemical conversion or refining. The biofuels a typical US driver is most likely to encounter are:

• Ethanol: an alcohol usually produced by fermenting crops such as corn or sugarcane. It is blended into gasoline and used in spark-ignition engines. • Biodiesel: a fuel made by chemically reacting vegetable oils, animal fats or recycled cooking grease with an alcohol. It is used in diesel engines, usually as a blend. • Renewable diesel: a diesel fuel made from similar fats and oils but processed with hydrogen in a refinery-style process. Chemically it closely resembles petroleum diesel. • Biogas and renewable natural gas: gaseous fuels from decomposing organic matter, used mainly in fleets with natural gas engines rather than in typical passenger vehicles.

So every biodiesel is a biofuel, but most biofuels are not biodiesel.

What Biodiesel Is

Biodiesel is produced through transesterification, a chemical reaction in which fats or oils react with an alcohol, usually methanol, in the presence of a catalyst. The result is a set of compounds called fatty acid methyl esters, often shortened to FAME, plus glycerin as a byproduct. The esters are the biodiesel.

Biodiesel can run in a diesel engine because its ignition behavior and energy content are close enough to petroleum diesel. It is not identical, though. It is chemically different from petroleum diesel, which is why blend limits, cold-weather behavior and storage practices matter. Raw vegetable oil or unprocessed waste grease is not biodiesel and does not meet biodiesel fuel standards.

Biodiesel and Renewable Diesel Are Not the Same

This is the distinction most likely to confuse diesel owners, because both fuels come from similar raw materials and both are often marketed as renewable or bio-based.

Biodiesel is an ester with oxygen in its molecular structure. That gives it different solvent, cold-flow and storage characteristics from conventional diesel, and it is normally sold as a blend with limits set by the vehicle manufacturer.

Renewable diesel, sometimes called hydrotreated vegetable oil or HVO, is processed until it is a hydrocarbon fuel very similar to petroleum diesel. In the US it can meet the same standard specification used for conventional diesel fuel (ASTM D975), which is why it can generally be used in diesel engines without the blend restrictions that apply to biodiesel. If a pump or fleet card mentions renewable diesel, do not assume biodiesel rules apply, and vice versa.

Side-by-Side Comparison

Fuel | Category | Engine type | How it is made | Typical use by drivers; Biofuel (general term) | Umbrella category | Depends on the specific fuel | Many processes from biological feedstocks | Not a fuel you buy by that name; always a specific product; Biodiesel (FAME) | Biofuel | Diesel | Transesterification of oils and fats | Blended into diesel, such as B5 or B20; B100 only where approved; Renewable diesel (HVO) | Biofuel | Diesel | Hydrotreating of oils and fats | Used like conventional diesel where available; Ethanol | Biofuel | Gasoline (spark ignition) | Fermentation of crops or biomass | Blended into gasoline, such as E10, E15 or E85 for flex-fuel vehicles

Reading Blend Labels at the Pump

Biofuel blends in the US are labeled with a letter and a number. The number is the approximate percentage of biofuel in the mix.

• B5: up to 5 percent biodiesel. Diesel fuel meeting the standard US specification may already contain biodiesel at this level, often without a separate label. • B20: between 6 and 20 percent biodiesel, covered by its own fuel specification (ASTM D7467). Many modern diesel vehicles are approved for B20, but not all. • B100: pure biodiesel, covered by the specification used for biodiesel blendstock (ASTM D6751). It requires specific manufacturer approval and is more common in fleets with dedicated fuel handling. • E10, E15, E85: ethanol blends for gasoline engines. These have nothing to do with diesel vehicles.

Which Differences Matter for Your Vehicle

If You Drive a Diesel

Biodiesel and renewable diesel are the biofuels relevant to you. The deciding factor is your manufacturer's approved blend limit, which is listed in the owner's manual and sometimes on the fuel door. Approval can vary by model year, engine and emissions equipment, even within the same nameplate, so check the documentation for your exact vehicle rather than relying on what another owner runs.

Using a blend above the approved limit may affect warranty coverage if a fuel-related problem occurs. Staying within the approved blend and buying from stations selling fuel that meets the applicable specification are the two most practical safeguards.

If You Drive a Gasoline Vehicle

Biodiesel is not for your engine under any circumstances. The biofuel you are likely already using is ethanol, blended into most US gasoline at around 10 percent. Higher blends such as E15 are approved for many newer vehicles, while E85 is only for vehicles designated as flex-fuel. Your owner's manual and fuel door will indicate which blends are allowed.

If You Manage a Fleet or Equipment

Higher biodiesel blends and renewable diesel are more common in fleet operations, where fuel is bought in bulk and stored on site. Here storage conditions, tank cleanliness, fuel turnover and cold-weather planning become as important as engine approval.

Practical Considerations When Using Biodiesel Blends

• Cold weather: biodiesel tends to thicken and form crystals at higher temperatures than petroleum diesel, and the effect grows with the blend percentage. In cold climates, suppliers often adjust blends seasonally or add cold-flow treatments. • Fuel filters: biodiesel acts as a mild solvent and can loosen old deposits in tanks and fuel systems. When a vehicle first switches to a higher blend, those deposits may clog the fuel filter sooner than usual. • Moisture and storage: biodiesel holds more water than petroleum diesel and is less stable over long storage periods. This matters most for vehicles or equipment that sit unused and for stored bulk fuel. • Fuel economy: biodiesel contains somewhat less energy per gallon than petroleum diesel, so higher blends can slightly reduce mileage. At low blends the difference is generally small enough to be hard to notice in everyday driving. • Older vehicles: some older diesel fuel systems used rubber components that can degrade with exposure to biodiesel. Owners of older vehicles should be especially careful to confirm compatibility.

Choosing by Situation

• Modern diesel car or truck, everyday driving: use conventional diesel or a biodiesel blend up to your manufacturer's approved limit, commonly B5 or B20. Renewable diesel is generally an option where it is sold. • Diesel vehicle in a cold climate: favor lower biodiesel blends in winter or rely on suppliers' seasonal winter blends; renewable diesel typically handles cold better than biodiesel of a similar blend level. • Diesel that sits for long periods: avoid storing high biodiesel blends for extended times, and consider conventional diesel or renewable diesel for vehicles used infrequently. • Older diesel of uncertain compatibility: stick with conventional diesel or low blends until you have confirmed that the fuel system is compatible. • Gasoline vehicle: ignore biodiesel entirely; follow your vehicle's guidance on ethanol blends. • Flex-fuel gasoline vehicle: you can choose between regular gasoline and E85; biodiesel still does not apply.

Common Misconceptions

"Biofuel" and "biodiesel" mean the same thing. They do not; biodiesel is one type of biofuel, and ethanol is another one aimed at a completely different engine type.

Any diesel engine can run on vegetable oil. Straight vegetable oil is not biodiesel and does not meet diesel or biodiesel fuel standards. Running it typically requires engine modifications and falls outside normal manufacturer approval.

Renewable diesel is just a fancy name for biodiesel. Although they share feedstocks, they are made differently and have different chemistry, which is why their usage rules differ.

If a fuel is a biofuel, it is safe for my car. Compatibility depends on the specific fuel, the blend level and your engine's approval, not on the biofuel label.

Bottom Line

Think of biofuel as the family name and biodiesel as one family member. For diesel owners, the decision usually comes down to choosing between conventional diesel, a biodiesel blend within the approved limit and renewable diesel where available. For gasoline owners, the relevant biofuel is ethanol. In every case, your owner's manual is the final word on which blends your specific vehicle can use.