In Mobil's Methanol-to-Gasoline (MTG) Process, two types of catalyst deactivation occur. The first type is reversible coking of the zeolite; the coke is burned off during regeneration, restoring activity. The second type is permanent deactivation of the zeolite. We have developed a dynamic simulation of the MTG process to investigate the interaction between these two types of deactivations. In our simulation, the rate of the coking depends on the amount of irreversible deactivation that had previously occurred. Also, the permanent deactivation occurs both during the reaction and catalyst regeneration. With this type of deactivation interaction, we were able to predict experimental observations in our pilot plant studies; in particular, the second cycle on a given catalyst is longer than the first cycle. We have used the model to compare the overall catalyst cycle life for both adiabatic and isothermal reactor simulations.