The structure and variance of the equatorial zonal circulation, as characterized by the atmospheric mass flux in the equatorial zonal plane, is examined and inter-compared in simulations from 9 CMIP3 coupled climate models with multiple ensemble members and the NCEP-NCAR and ERA-40 reanalyses. The climate model simulations analyzed here include 20th Century (20C3M) and 21st Century (SRES A1B) simulations. We validate the modeled zonal circulations by comparing them with those in the reanalyses. We then examine the variability of the circulation, its changes with global warming, and the associated thermodynamic maintenance. The relative agreement between climate models and reanalyses and the agreement between individual models are evaluated using second-order space-time climate difference statistics.