The use of model bio-oil from pyrolysis biomass as a fuel was improved by forming diesel microemulsion using rhamnolipid (RL) as the surfactant. After microemulsification, synthetic bio-oil components were solubilized in different positions of the microemulsion. Water and some hydrophilic substances were solubilized in the hydrophilic core of the microemulsion, glyoxal, and vanillin in the palisade layer, and guaiacol in the diesel continuous phase. The bio-oil components species and their solubilization positions in the microemulsion fuel system had considerable effect on properties of the fuel, e.g., degradation/combustion characteristics as determined by thermogravimetric analysis.