Sensitivity analysis of rate constants of Weekman's riser kinetics has been carried out using CATCRAK (A process simulator for an integrated FCC-regenerator system: Ind. Eng. Chem. Res. 34 (1995) 3737). The rate constants were varied to within +/-50% of their original estimates. The variation in the rate constant was plotted against gasoline yield and overall conversion. Based on the comparisons made between various plots, the 20 rate constants of Weekman's riser kinetics were grouped in five different categories. The advantage of such a grouping in fine-tuning the simulator predictions has been illustrated using a commercial example. Finally, a simplified model for the estimation of heat of cracking reactions has been presented. The estimated values of heat of cracking reaction (similar to600 kJ/kg) compared well with the reported data. (C) 2002 Elsevier Science B.V. All rights reserved.