Radiocarbon activity of fuels is a direct analog to the biogenic fraction of carbon in the fuel. The amount of radiocarbon in a fuel sample may be determined by liquid scintillation direct analysis if the sample is relatively transparent to ultraviolet light. However, many biofuels are colorful which adversely affects the counting efficiency of this technique and therefore the precision which the biofuel blend level may be determined. In such cases, decolorization may be an approach to improve measurement precision. Here, we present the effectiveness of several decolorization techniques for different fuel types. For some fuels, decolorization impacted the radiocarbon content of the sample; therefore, caution is necessary to ensure reliable assessment of biofuel blend levels.