Four different types of large-port mordenite were studied. Three of these catalyst samples were dealuminated by treatment with nitric acid, and the fourth type was a series of commercially available dealuminated mordenites. The methanol conversion and propene oligomerization productivities and selectivities of these dealuminated mordenites were investigated on a laboratory scale at typical industrial reaction temperatures and pressures. The optimum catalyst morphology and degree of dealumination needed for maximum productivity were found to be similar for both methanol conversion and propene oligomerization. High catalytic productivities were obtained with mordenite which had been hydrothermally dealuminated or with small crystallites which had been synthesized or dealuminated in such a way as to minimize the amount of extra-framework aluminum in the mordenite pores.