The present study investigates the effects of the changes of the catalyst to feedstock ratio (C/O) on FCC cracking using a Y-zeolite-based catalyst. Experiments are developed in a CREC Riser Simulator. This bench-scale mini-fluidized batch unit mimics the operating conditions of large-scale FCC units as follows: It uses temperatures ranging from 510 to 550 degrees C and reaction times from 3 7 s. For every experiment, 0.2 g of 1,3,5-TIPB is contacted with a 0.12-1g catalyst amount. This is done to achieve a C/O ratio in the range of 0.6-5. Experiments show the effects of increasing the C/O ratio on 1,3,5-TIPB conversion, coke formation, and product selectivity. On this basis, a mechanism involving single catalyst sites for cracking and two sites for coke formation is considered. Coke formation is postulated as an additive process involving coke precursor species, which are either adsorbed on sites in the same particle or adsorbed in close sites in different particles. The proposed mechanism helps explain the results obtained, introducing a rationale-for the selection of optimum C/O ratios to yield the highest possible 1,3,5-TIPB conversions with controlled amounts of coke formation. It is anticipated that the findings of this study will have a significant influence on the selection of an optimum C/O ratio for the design and operation of the most advanced FCC risers and downers.