Process for the preparation of olefins comprising reacting an oxygenate and/or olefinic feed in a reactor in the presence of a molecular sieve catalyst to form a mixture which comprises olefins and at least partially coked catalyst; separating olefins and at least partially coked catalyst as obtained; passing the at least partially coked catalyst to a regenerator; introducing into the regenerator an oxygen-containing gas to regenerate the at least partially coked catalyst, thereby producing a gaseous mixture and at least partially regenerated catalyst; analyzing the at least partially regenerated catalyst to control the burning rate of the coke present on the at least partially coked catalyst in the regenerator by adjusting one or more conditions of the regeneration of the at least partially coked catalyst on the basis of the analysis of the at least partially regenerated catalyst; and passing the at least partially regenerated catalyst to the reactor.