The gas phase MTBE synthesis reaction was studied on a number of zeolite catalysts, in order to obtain a better understanding of the impact of acidity on zeolite activity for MTBE formation away from thermodynamic equilibrium limitations. The catalysts investigated included a series of dealuminated HY zeolites with different acid properties. In addition, H-ZSM-5, an amorphous silica-alumina, and Amberlyst-15 resin were investigated for comparison. An increase in acidity of the HY zeolites produced by dealumination was found to result in a significant enhancement in the intrinsic activity for MTBE formation. The ratio of extra-lattice to lattice Al appears to be an important parameter for determining the catalytic behavior of zeolites for this reaction.