The objectives of this study were to evaluate statistically the effects of coprocessing parameters on liquefaction yields, to determine the key process variables affecting the oil+gas, oil and asphaltene yields and total conversion. A statistical experimental design based on Second Order Central Composite Desing was planned fixing the liquefaction period at 1 h. Parameters such as temperature, initial cold pressure, tetralin/(lignite+sawdust) and sawdust/lignite ratios coded as x(1), x(2), x(3) and x(4), respectively, were used. The parameters were investigated at five levels (-2, -1, 0, 1 and 2). The effects of these factors on dependent variables, namely, oil+gas, oil and asphaltene yields and total conversion were investigated. To determine the significance of effects, the analysis of variance with 99.9% confidence limits was used. It was shown that within the experimental ranges examined, temperature and sawdust/lignite ratio were the variables of highest significance for oil+gas yields, oil yields and total conversion. (C) 2002 Elsevier Science B.V. All rights reserved.