Seismic reservoir monitoring is a new technology that involves interpreting differences between different generations of 3-D seismic data in terms of changes in reservoir properties over time. A vast number of 3-D seismic surveys are repeated, in whole or in part, for reasons other than reservoir monitoring. In this paper, we cross-equalize two off-the-shelf migrated datacubes over a Gulf of Mexico field with favorable reservoir properties, to see whether their time-lapse nature can be exploited for reservoir monitoring purposes. Key elements in the processing flow include spatial realignment to a common grid, wavelet equalization by L2 matched-filtering, warping to compensate for different stacking/migration velocities, and amplitude balancing. A balance is struck between global and local operators to ensure a clean cross-equalization result without inadvertently removing changes due to fluid production.