Increased production and use of renewable hydrocarbons has created a need for accurate quantification of the biobased carbon content of hydrocarbon fuels. The blend percentages of conventional biofuels (such as biodiesel and ethanol) can be quantified by numerous methods such as gas chromatography and infrared spectroscopy. Distinguishing the biobased content of a purely hydrocarbon fuel, however, is more difficult. In this study, a single-blind trial was conducted to assess the accuracy and precision of accelerator mass spectrometry (AMS) radiocarbon analysis of the biobased carbon content of hydrocarbon fuels. Test samples with known biobased carbon contents ranging from 0 to 10 wt% were sent to four labs for analysis by ASTM D6866-16 Method B. Blank correction of the test results was found to improve measurement accuracy through the reduction of lab-specific systematic error. Favorable precision, accuracy, and a limit of detection were determined. This study strongly supports radiocarbon analysis by AMS as an accurate and reliable method for quantifying the biobased carbon content of hydrocarbon transportation fuels.