Supply Reef is a conical submarine volcano in the northern Mariana Islands that rises to within 8 m of the surface. The andesitic seamount lies about 17 km NW of the Maug Islands, the emergent summit of a submarine volcano that is joined to Supply Reef by a low saddle at a depth of about 1,800 m. Supply Reef was mapped as Quaternary; living corals on the crater rim suggest that it is either dormant or extinct (Corwin, 1971). Submarine eruptions previously attributed to this volcano based primarily on acoustic data have been reassigned to Ahyi Seamount, which was unknown at the time of those reports.