The performance of a coked fluid catalytic cracking catalyst (0.56 wt % coke on catalyst) has been determined and compared to that of a fully regenerated catalyst by cracking of a Hydrowax feedstock in the microriser equipment. The activity of the coked catalyst is lower, but still significant, and the selectivity is similar to that of the regenerated catalyst. A kinetic analysis shows that the activity of the coked catalyst is constant: it is not further decreased by additional coke deposition. The kinetic model can be used to predict the performance of a mixture of the coked and regenerated catalyst because it behaves like a physical mixture of the two catalysts The application of such mixtures in industrial operation, as in the recently developed UOP X-design, increases process flexibility; the temperature of the stripper and the riser inlet and. the associated reaction selectivities can be changed without changing the overall heat balance of the process.