The depolymerization-liquefaction reactions of representative polystyrene and styrene-butadiene co-polymer (non-vulcanized SBR) samples were systematically investigated as a function of processing variables, i.e. temperature (350-450 degrees C), time (15-120 min), H-2 pressure (500-2500 psig), and the presence of catalysts. Two solid superacids, i.e. Fe2O3/SO42-and ZrO2/SO42-, which differ in acidity were used in the study. The detailed composition of products was determined by GC/MS. Typical products from a polystyrene sample (average MW, 280 000) contained benzene, toluene, (C-2-C-5) alkyl- and alkenylbenzenes, 1,3-diphenylalkanes and triphenylalkanes, accompanied by some indanes, tetralins, naphthalenes and polyphenyls, whereas products from non-vulcanized SBR (MW, 140 000) contained, in addition to the above, C-5-C-9 paraffins and cycloparaffins, (C-5-C-8) alkyl- and alkenylbenzenes, cyclopentylbenzenes, and cyclohexylbenzenes. The changes in product composition as a function of the above processing variables were determined and conditions for preferential (> 85 wt.%) production of gasoline-range liquid fuels established. The observed change in composition as a function of reaction time and temperature allowed for elucidation of mechanistic aspects of high-temperature depolymerization-liquefaction processes, including the role of catalytic effects.