O-17-H-1 double resonance NMR spectroscopy was used to study the local structure of zeolite H-Mordenite. Different contact times were used in cross-polarization magic angle spinning (CPMAS) NMR, CP rotational-echo double resonance (CP-REDOR) NMR, and heteronuclear correlation (HETCOR) NMR spectroscopy to distinguish between Bronsted acid sites with different O-H distances. The accessibility of the various Bronsted acid sites was quantified by adsorbing the basic probe molecule trimethylphosphine in known amounts. On the basis of these experiments, locations of different Bronsted acid sites in H-Mordenite (H-MOR) were proposed. The use of O-17 chemical shift correlations to help assign sites is discussed.