Biodiesel is a liquid which varies in color between golden and dark brown depending on the production feedstock. The lighter colored fuel is typically derived from unused crop oil grown specifically for this use. The darker fuel is more common with oil that has been used in a restaurant fryer and is then recycled rather than dumped making it even more environmentally friendly. ​

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When biodiesel is cooled below a certain point, some of the molecules aggregate and form crystals. As biodiesel is cooled further it will gel and then solidify. Biodiesel produced from oil varieties such as canola seed starts to gel at approximately −10 °C (14 °F).  Several techniques can be used to overcome this fuel's cold sensitivity. The fuel tank and lines can be insulated and/or heated using either electric heat elements or engine coolant circulated​ through the tank and lines. In extremely cold climates a second fuel tank can be added and the fuel tanks can be switched over when the fuel is sufficiently warm. A similar method is used to operate diesel vehicles using straight vegetable oil.