Catalytic and thermal degradation of waste expandable polystyrene (WEPS) have been studied in a semi-batch reactor with continuous flow of nitrogen to achieve greater oil yield and maximize styrene monomer recovery. Effect of temperature, nature of catalyst and its size, reaction time of catalytic pyrolysis, and effect of repyrolysis have been also investigated. Higher reaction temperature favors the oil yield and also decreases the reaction time with maximum styrene selectivity (76.31 wt %) at 450 degreesC. Among the catalysts studied, solid base BaO is found to be the most efficient and increases the styrene selectivity (84.29 wt %) significantly at a reaction temperature of 350 degreesC in comparison to thermal and acid catalytic degradation. Modified catalyst Fe-A/Al (A = basic material) also shows better activity than Fe2O3 or Fe/Al. Increase in the size of the catalyst and repyrolysis decrease the oil yield, and styrene production also decreases on repyrolysis.