The middle Miocene d18O enrichments from deep-sea proxy data and eustatic sea level falls are traditionally attributed to expansion of East Antarctic Ice Sheet. Interpretations of such data have led many to conclude that West Antarctic Ice Sheet was not well developed until the late Miocene. In such a scenario, middle Miocene glaciation on the Ross Sea shelf would have had to be minimal, such as in the form of ice caps, for it to be consistent with proxy data, because West Antarctica constitutes a major part of the drainage basin for the Ross Sea. New seismic-stratigraphic analysis of the Ross Sea outer continental shelf shows that at least five grounding events (ice-sheet advances into the marine environment) occurred in the middle Miocene. We interpret these grounding events to have been shelf-wide because they exhibit progradation directed offshore and the associated strata thicken basinward. Ice cap glaciation should have thickest subglacial strata rimming topographic highs, and possibly exhibit a radial progradation direction. This therefore suggests that the West Antarctic Ice Sheet may have been more vigorous in the middle Miocene than has previously been deduced from proxy data.