Biodiesel is better than diesel for the climate, cutting lifecycle greenhouse gas emissions by up to 74% when used in pure form. But the full picture is more nuanced. Biodiesel carries trade-offs in energy content, cold weather reliability, engine compatibility, and land use that make the answer depend on how and where you plan to use it.
Greenhouse Gas Emissions
The biggest advantage biodiesel holds over petroleum diesel is its carbon footprint. A lifecycle analysis by Argonne National Laboratory found that pure biodiesel (called B100) produces 74% fewer greenhouse gas emissions than conventional diesel when you account for everything from production to combustion. That’s a significant gap, and it’s the main reason biodiesel gets promoted as a cleaner alternative.
The reason is straightforward: biodiesel is made from plant oils or animal fats that absorbed carbon dioxide while growing. When that fuel burns, it releases roughly the same CO2 back into the atmosphere. Petroleum diesel, by contrast, releases carbon that’s been locked underground for millions of years, adding new carbon to the cycle. The reduction isn’t 100% because growing, harvesting, and processing biodiesel feedstocks still requires fossil fuel energy.
Air Quality: A Mixed Picture
At the tailpipe, biodiesel blends of 20% (B20) reduce particulate matter, carbon monoxide, and total hydrocarbons by 15% or more compared to petroleum diesel. They also cut emissions of toxic compounds, including certain aldehydes and cancer-linked particles called polycyclic aromatic hydrocarbons. For anyone living near highways, truck depots, or bus routes, these reductions translate directly into cleaner air.
There’s one notable exception: nitrogen oxides, or NOx. These compounds contribute to smog and respiratory problems, and biodiesel actually increases them. A B20 blend raises NOx emissions by about 2% on average, while pure biodiesel pushes them up roughly 10% in heavy-duty engines. Under high-load conditions, the increase can be even steeper. This is biodiesel’s most significant air quality drawback, and it’s one reason emissions regulations make the fuel a complicated choice in areas already struggling with smog.
Energy Content and Fuel Economy
Biodiesel contains less energy per gallon than petroleum diesel. Standard low-sulfur diesel holds about 128,500 BTU per gallon, while pure biodiesel comes in at roughly 119,550 BTU. That’s about 7% less energy, which means you’ll burn more fuel to cover the same distance. In practical terms, a truck running on B100 might see its fuel economy drop by a similar percentage.
Most drivers never use pure biodiesel, though. The common B20 blend (20% biodiesel, 80% petroleum diesel) contains about 126,700 BTU per gallon, only about 1.4% less than regular diesel. At that level, the difference in fuel economy is small enough that most people wouldn’t notice it during normal driving.
What It Costs
Price used to be a clear disadvantage for biodiesel, but the gap has essentially closed. Recent national averages show B20 and standard diesel both selling at $3.74 per gallon. Prices fluctuate by region and season, and biodiesel availability is still more limited, particularly in rural areas. But for drivers who can find it, the cost argument against biodiesel has largely disappeared.
Cold Weather Performance
This is where biodiesel struggles most. All diesel fuels thicken in cold weather, but biodiesel does it sooner. Pure biodiesel begins forming waxy crystals (its “cloud point”) at temperatures ranging from -3°C to 15°C (roughly 27°F to 59°F), depending on the feedstock it was made from. Soy-based biodiesel handles cold better than palm-based biodiesel, but neither matches petroleum diesel’s cold weather tolerance.
Below the cloud point, the fuel can clog filters and fuel lines, potentially leaving you stranded. This is why B20 blends are far more common than B100 in colder climates. Blending with petroleum diesel lowers the cloud point considerably. If you live somewhere with harsh winters, running high-percentage biodiesel year-round is impractical without additives or heated fuel systems.
Engine Compatibility and Warranties
You can’t just pour pure biodiesel into any diesel engine and expect everything to work perfectly. Many engine manufacturers limit their warranty coverage to diesel fuel containing no more than 5% biodiesel. Some newer engines are approved for B20, but B100 compatibility remains uncommon in standard factory warranties.
The concern isn’t just theoretical. Biodiesel is a solvent, and in older engines it can degrade rubber seals and hoses that weren’t designed for it. It can also loosen deposits in fuel tanks and lines, sending debris into filters. Engines built or retrofitted for biodiesel handle it fine, but switching an older vehicle to high-blend biodiesel without checking compatibility risks expensive repairs that your warranty won’t cover.
The Land Use Problem
Biodiesel’s environmental benefits get complicated when you zoom out from the tailpipe. Growing the crops to produce biodiesel requires land, and the EPA has found that biodiesel’s land use footprint is substantial. Producing a billion gallons of biodiesel required between 780,000 and 1.5 million acres of cropland in 2018, roughly double the land intensity of corn ethanol on a per-gallon basis.
This matters because converting forests, grasslands, or wetlands to cropland releases stored carbon and destroys habitat. Globally, palm oil-based biodiesel has been linked to tropical deforestation in Southeast Asia. Soybean-based biodiesel, dominant in the U.S., drives demand for agricultural land that might otherwise support food production or remain as natural habitat. Biodiesel made from waste cooking oil or animal fats sidesteps this problem almost entirely, since it uses materials that would otherwise be discarded. The feedstock source makes a dramatic difference in whether biodiesel’s climate benefits hold up under scrutiny.
Which Blend Makes the Most Sense
For most drivers, B20 hits the practical sweet spot. It delivers meaningful emissions reductions, works in cold weather far better than pure biodiesel, costs the same as regular diesel, and falls within the blend limits that more manufacturers support. You lose barely any fuel economy, and the engine compatibility risks are minimal in modern vehicles.
Pure biodiesel makes the strongest environmental case on paper, but its real-world limitations in cold tolerance, energy content, and engine compatibility confine it mostly to fleet vehicles in warm climates, where operators can manage fueling infrastructure and maintenance schedules around its quirks. If you’re weighing the switch, the feedstock matters too. Biodiesel made from waste oils delivers the climate benefits without the land use costs. Biodiesel made from virgin palm oil may do more environmental harm than good once deforestation enters the equation.