The observed Bouguer anomalies on the volcanic islands in Western Samoa (Savai'i and Upolu) and American Samoa (Tutuila and the Manu'a Islands), and the free air anomalies at sea, are consistent with island platforms of density 2.4 Mg/m3(pyroclastic basaltic materials) containing cores of density 2.9 Mg/m3(basalt), and varying degrees of lithospheric depression. The maximum depression of about 2 km occurs below the western islands and is practically zero below the Manu'a Islands at the extreme eastern end of the island chain.