The effects of catalyst acidity and the restricted reaction volume afforded by HZSM-5 on the volatile cracking products derived from poly( styrene) are investigated. Three catalysts : silica/alumina, HZSM-5, and sulfated zirconia, were employed as cracking catalysts. Styrene, which is the principal radical depolymerization product from poly(styrene), is a minor catalytic cracking product. The most abundant volatile product generated by catalytic cracking is benzene. Alkyl benzenes and indanes are also detected in significant yields. Various thermal analysis techniques are employed to obtain volatilization activation energies for polymer-catalyst samples and to elucidate probable reaction pathways. Detected products are explained by reaction mechanisms that begin with protonation of poly( styrene) aromatic rings.