The degradation kinetics of polystyrene (PS) in supercritical benzene was studied at various temperatures (300-330 degreesC) at 5.0 MPa. The time evolution of the molecular weight distributions was obtained by analyzing the samples with gel permeation chromatography. The evolution was modeled with continuous distribution kinetics by assuming that the degradation rate coefficient varied linearly with molecular weight. The activation energy of the rate coefficient was determined to be 13.8 kcal/mol. The degradation rate coefficients obtained in supercritical benzene were substantially higher than the rate coefficients observed for degradation of PS in subcritical solvents at high pressures and in solvents at normal pressures. This significant enhancement in the degradation rate may be due to enhanced diffusivity in supercritical fluids.