For the first time, a comprehensive comparison of the intrinsic activities of solid acid catalysts in terms of turnover frequency (TOF) is reported for the gas-phase esterification of acetic acid with methanol. The catalysts studied included a zeolite (H beta), two modified zirconias (sulfated zirconia, SZ; and tungstated zirconia, WZ), and an acidic resin-silica composite (Nafion/silica, SAC-13). Activities on a per weight basis decreased in the following order: H beta similar to SAC-13 >> SZ > WZ at 130 degrees C. However, on a rate-per-site basis (TOF), all catalysts showed comparable activities. The TOF results suggest that the acid sites of these catalysts have similar capacity for effectively catalyzing esterification. All catalysts deactivated to a quasi-steady-state rate with TOS. Regeneration experiments suggested that catalyst deactivation was due mainly to site blockage by carbonaceous deposits. Selective poisoning experiments showed that the reaction predominately took place on Bronsted acid sites.