A simulation study of thermal cracking of recycled gases or mixtures of C2-C6 hydrocarbons downstream of a hydrogenation process is presented. A kinetic and mathematical model was derived on the basis of which a computer model was developed in CHEMCAD environment. Validation of the model was performed by comparing the results of numerical experiments with measurement data of cracked gas in an industrially operated furnace. A detailed sensitivity study is carried out to analyze the effects of feed components and operating parameters on desired product yields as well as on the furnace online operation period. The developed model is applicable for operational analysis of cracking furnaces but it can be utilized also for examination of profitability improvement opportunities originating either from modifying feed composition or alteration of operating parameters. (C) 2006 Elsevier B.V. All rights reserved.