With conventional diesel fuels, the inherent energy content of the fuel, measured typically in BTUs per gallon, is the largest factor in the fuel economy, torque, and horsepower delivered by the fuel. The energy content of conventional diesel can vary up to 15% from supplier to supplier or from summer to winter. This variability in conventional diesel is due to changes in its composition, and these changes are determined by the refining and blending practices.

With biodiesel, or B100, the refining and blending methods have no significant effect on energy content. The reason B100 does not vary much is because the energy content of the fats and oils used to make biodiesel do not vary nearly as much as the components used to make diesel fuel from petroleum. Cetane Number is a measurement of the combustion quality of diesel fuel during compression ignition. It is a significant expression of diesel fuel quality among a number of other measurements that determine overall diesel fuel quality.

Most of the B100 made today that meets D6751 has a cetane number higher than 47. This is compared to the minimum of 40 for highway diesel fuel, whose national average is between 42 and 44. Therefore, biodiesel has a higher cetane number than most U.S. diesel fuel, which is believed to provide easier starting and quieter operation. Highly saturated B100, such as animal fats and used cooking oils, can have a cetane number of 70 or higher.