The measured viscosity, water content and density of the non-catalytic and catalytic rice husk bio-oil is also shown in Table 6. The water content for the catalytic runs increases in the bio-oils. These indicate the catalysts are involved in the formation of water through reactions such as cracking and dehydration. The highest value of 55.56% was obtained for ZSM-5, which indicates its stronger dehydration tendency compared to the other catalysts, due to its stronger acidity [52]. Oasmaa et al. reported that the density is a function of water content [58]. The density of the bio-oil decreases for the catalytic runs in comparison to the non-catalytic run, which can be attributed to the increase in the water content. Ji-lu found the density of rice husk bio-oil is 1190 kg/m3at a water content of 25.2% [20], and Lu et al. obtained a value of 1140 kg/m3 at a water content of 28% [23]. In this study, the density of the non-catalytic pyrolysis oil is measured to be 1065 kg/m3at 52.6% water content. The result from the viscosity measurements shows that the catalysts have an effect of reducing the viscosity on all of the runs. The low viscosity values for all, suggest that the viscosity is greatly influenced by the water content in the sample, as suggested by Nolte and Liberatore [54].