to lower char yield. The gas yield had a negative relationship with bio-oil heating value and viscosity, implying that the higher the gas yield, the lower the bio-oil HHV and viscosity. This is in good agreement with the results from Figure 2. In addition, it was also found that the correlation coefficient of the total bio-oil and the HHV of the heavy bio-oil was lower than -0.8. Therefore, the HHV and the viscosity of the heavy bio-oil reduced with the total bio-oil yield because the total bio-oil yield, HHV and viscosity had the correlation coefficients of higher than 0.9