The properties of slurries made of pyrolysis oil mixed with wood, char or ground char were investigated with respect to phase transitions, rheological properties, elemental compositions, and energy density. Also the pumping properties of the slurries were investigated at temperatures of 25, 40 and 60 degrees C and solid loadings from 0 to 20 wt%. The phase transitions of the wood slurry samples were observed at lower solid loadings compared to the char slurry samples. The apparent viscosity of the slurry samples was found to be considerably impacted by solid loading (0-20 wt%) and temperature (25-60 degrees C), especially in the phase transition region. The slurry viscosities with 20 wt% char loading, 20 wt% ground char loading and 15 wt% wood loading (at a shear rate of 100 s(-1)) are 0.7, 1.0 and 1.7 Pa.s, respectively at 60 degrees C and these values increases 1.2-1.4 times at 40 degrees C and 3-4 times at 25 degrees C. The wood, char and ground char slurry samples with 5-20 wt% solid loading obtain a volumetric energy density of 21-23 GJ/m(3). The slurry sample with 20 wt% ground char having a d(80) of 118 mu m was pumped successfully into a pressurized chamber (0-6 bar) while plugging appeared when the slurry samples with 15 wt% char having a d(80) of 276 mu m was pumped into the pressurized chamber. (C) 2013 Elsevier Ltd. All rights reserved.