In this study, the effects of various experimental parameters on the liquefaction yields of a biomass waste material, namely pine barks, were investigated statistically. The key parameters investigated were temperature, pressure, solvent to pine bark ratio and tetralin to solvent mixture ratio. A statistical experimental design based on second order central composite rotatable design was planned fixing the liquefaction period at I hour. The experimental design was done at five levels and the studied ranges for temperature, pressure, solvent to pine barks ratio and tetralin to solvent mixture ratio were 300-400 degrees C, 10-50 atm, 1/1-5/1 and 0/1-1/1, respectively. The effects of these factors on dependent variables, namely, oil+gas, asphaltene and preasphaltene yields and total conversion were studied in detail. To determine the significance of effects, the analysis of variance with 99.9% confidence limits was used. The model equations for dependent variables were also developed and an optimization study was done. (c) 2005 Published by Elsevier B.V.