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Biodiesel is currently less regulated than regular diesel fuel. Ensure the fuel meets the biodiesel quality specifications addressed by ASTM D-6751. This can be accomplished by carefully selecting your supplier. "Request fuel from a BQ-9000 certified marketer, or from a BQ-9000 accredited producer," says Pearson.

Energy content
Energy content of diesel fuel is measured in BTUs per gallon. The higher the energy content, the more power you can get out of your fuel. No. 2 diesel typically contains 130,000 BTU/gal.

Ryan Central has looked at the cost per BTU of its diesel fuel. "You look at all of your costs performance-wise," says Fell. "A lot of times, by using a higher BTU fuel content, you are going to come out ahead. Ultimately, you will have a lower cost per BTU."

One way to gauge how much BTU a fuel contains is by the API gravity measurement. "API gravity is a measure of fuel density, and affects the heating value (BTUs) of a fuel," says Bob Theisen, manager, technical services, CHS.

"It can also be used to predict the relative viscosity of a diesel fuel," Harvey adds. "As a rule of thumb, the lower the API gravity, the higher the energy density, viscosity and mass density of the fuel." For example, a diesel fuel with an API gravity of 30 will generally be higher in energy content, more viscous and heavier on a weight per gallon basis compared to a fuel with a 40 API gravity.