In a new study, researchers from Woods Hole Oceanographic Institution used highly accurate radiocarbon testing on samples from 20 different biodiesel blenders to determine the biodiesel content of their fuel (so-called “splash blenders” mix pure biodiesel and diesel together before selling it at the pump).

The study found that blends sold as B20 biodiesel (20% biodiesel, 80% diesel) varied from 10% to 74% in actual biodiesel content.

“It’s a huge problem for the industry,” says Teresa Alleman of the National Renewable Energy Laboratory, who recently completed a study showing that biodiesel manufacturers have improved the overall quality of pure biodiesel over the past year. If consumers pay a premium for biodiesel that they aren’t getting, she says, public confidence could be shaken. Also, blenders receive a tax credit based on the amount of biodiesel used, which could mean some sellers have received larger credits than they merit.

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