Supply Reef is a submerged circular reef of volcanic origin in the Northern Mariana Islands chain, about 10 kilometres (6 mi) NW of the Maug Islands. Presently, this igneous seamount is roughly 8 metres (26 ft) below the ocean's surface and about 100 m (300 ft) in diameter. Apparent episodes of submarine volcanism were noted on December 22–24 and 26–27 in 1989.

Volcanic and seismic activity has been noted, as well as hard and soft corals.