ABSTRACT: Mid-Pliocene low-latitude Pacific faunal (planktic foraminifer) sea surface temperature (SST) estimates are normally based upon theModern Analog Technique (MAT). In the Eastern equatorial Pacific (EEP), where upwelling of cool water predominates, MAT can be used to discern both cooling and warming in Neogene records. SST today is ~30°C in the western equatorial Pacific (WEP) warm pool, the upper limit of the modern calibration data, and past warming above that level is difficult to assess using faunal methods. Mid-Pliocene fossil samples from the WEP have been analyzed using several variations ofMAT with different outcomes and associated levels of confidence. While SST above ~30°C in the WEP during the mid-Pliocene cannot be ruled out due to the limitations of the method, temperatures this warm seem unlikely. In addition to the mid-Pliocene, planktic foraminifer assemblages from the coretop, last glacial maximum, last interglacial and the penultimate glacial (Marine Isotope Stage 6) show striking similarity to each otherwhich suggests little to no change in the region between times of global climate extremes. There is generally good agreement between theMg/Ca paleothermometer and MAT derived faunal SST estimates. Both suggest stability of the WEP warm pool.