A new method based on liquid scintillation counting (LSC) was developed to determine the biocarbon content in liquid fuels via radiocarbon analysis. The method has a simple and straightforward procedure that requires no sample preparation, making it well suited for use in a refinery laboratory setting. Using the gasoline, diesel, and jet fuel blends made from renewable naphtha and diesel in petroleum (ranging from 0.5 to 100%), we demonstrate that moderately colored samples and sample luminescence do not influence the accuracy, nor does the method require any additional sample preparation. Statistical analysis of the data shows a very good correlation between the LSC method and accelerator mass spectrometry (AMS), with a sub 1% biocarbon detection limit for the LSC method.