Sipilae ` et al. [10] investigated the bio-oils from hardwood, softwood and straw by flash pyrolysis in an atmospheric fluidized bed. It was found that the viscosities were reduced in the bio-oils with higher water content and less water insoluble components. Viscosity was also affected by alcohols: an addition of 5 wt% methanol into hardwood pyrolysis oil with low methanol content decreased its viscosity by 35%. The straw oil is less viscous and had the highest methanol content of 4 wt%.