A mathematical model of a flow-reversal reactor is presented and analysed. The methanol synthesis is taken as an example. The range of parameters is established for the pseudo-steady-state operation of the reactor. An approximate method for the prediction of flow-reversal reactor parameters is proposed. A maximum cycling time is found to be the most important parameter. The method is based on a widely accepted approximation of the speed of moving reaction front as a ratio of heat capacity of gas to the heat capacity of a catalyst bed as well as concentration and temperature profiles in the steady state. The predicted trends are compared with numerical results and satisfactory agreement is found. The maximum cycling times obtained should be considered as an upper bound.