We examine the Gravity Recovery and Climate Experiment (GRACE) data and output from an ocean model to quantify mass fluctuations for the Pacific, Atlantic, and Indian Ocean basins from August 2002 until December 2008. The monthly spatial mean is removed to study interbasin mass exchange. We find a seasonal exchange of mass between the Atlantic and Pacific that is similar to one documented previously, although the amplitude observed by GRACE is about 20% lower than that simulated by an ocean model. There are also significant fluctuations with periods longer than 1 year. We find large interannual exchanges in 2005 and 2007, with GRACE observing yearly averaged mass anomalies in the Pacific that are about 30–40% larger than simulated by a model. This is shown to be from significant interannual mass losses from the Indian Ocean that are observed by GRACE but not simulated by the model. A longer run of the model, from 1976 to 2008, suggests that such interbasin mass exchanges are a regular occurrence and can last for as long as a couple of decades.