The density structure of the lithospheric and sublithospheric oceanic mantle is assessed with an integrating methodology that incorporates mineral physics, geochemical, petrological, and geophysical data. Compressibility, partial melting, and compositional layering are considered in addition to the standard thermal modelling. The results indicate that due to differences in the degree of melt depletion and crust segregation, the depth-averaged density of old oceanic plates with thermal thicknesses of ∼105 ± 5 km is always lower than the density of the underlying sublithospheric mantle. Moreover, representative depth-averaged density contrasts between the plate and the adiabatic mantle Δρ, do not exceed values of ∼40 kg m-3, in contrast to what is assumed (Δρ > 70 kg m-3) in many geodynamic models. Thus, the role of Δρ in triggering/assisting processes such as subduction initiation may be less critical than previously thought.