The results of the thermal and catalytic reactions of lignin model compounds are used in thea prioriprediction of its liquefaction. Lignin was defined probabilistically as an ensemble of single ring aromatics with substituents on each of their six ring positions. Elements in a substituent vector x1, for each ring position i, were matched into all possible combinations to describe lignin. Initial number fractions, or probabilities, for each vector element were ascertained through inspection of lignin structural data. The reaction of lignins altered the probabilities within each substituent vector, and reaction products were also calculated by matching all combinations of vector elements for each ring position. Model compound results provided the identities and rates of change of vector elements.