A simplified four-lump model for fluid catalytic cracking (FCC) as reported in the literature has been examined. The model, which relates the coke yield to other yields, is important to FCC operation but requires intensive data analyses. In this article, a new methodology that can validate the model and substantially simplify the data treatments is proposed. The method is applicable to both steady-state FCC riser cracking and unsteady-state microactivity tests (MAT). An explicit expression, derived for the coke yield as a function of conversion, is shown to describe the reported data well. The method is independent of the catalyst decay function and the reaction order of gas oil cracking. This enables the model to be applicable to many systems, even noncatalytic pyrolysis. A case study of the model, which uses the proposed method, suggests that for a given feed-catalyst system the relative rates of coke formation from either gasoline or gas oil may be the same for different reactors.