Abstract Two methods — collection of empirical subsidence data for aseismic ridges and observation of the increase in height of oceanic volcanoes with increasing lithospheric age — are used to try to discriminate between the thermal models for the oceanic lithosphere of McKenzie (1967), Parker and Oldenburg (1973), and Crough (1975). Although the volcano height data indicate that thickening of the lithosphere does occur, neither method is precise enough to allow preferential selection of one model over another.