The use of methyl tertiary butyl ether (MTBE) as a gasoline additive has resulted in serious environmental problems following spills and leaks, primarily due to MTBE's high solubility in water. Remediation technologies have involved air stripping, advanced oxidation, and sorption on granular activated carbons (GAC). Hydrophobic zeolites, such as silicalite, dealuminated Y, mordenite, and beta, have been of interest in recent studies for the removal of MTBE from water. Some of these materials have shown a better performance than GAC particularly in the microg/L range. We made Monte Carlo and molecular dynamics simulations of the adsorption of pure MTBE in silicalite, mordenite, and zeolite beta with different Na+ loadings at room temperature to reveal the factors affecting the adsorption process. The results show that although the three zeolites studied here have similar pore volumes, the pore structure of zeolite beta causes a significant difference on the predicted amount of MTBE adsorbed. It was found that the position of the Na+ cations has an important effect at lower pressures. Within the range of [Na+] studied, the amount of Na+ was not found to be critical on the adsorption capacity of any of the zeolites studied, except at very low pressures in silicalite and zeolite beta.