The sensitivity of pressure- and temperature-dependent thermal conductivity (k:W/m/K) and the thermal expansivity (&agr;:1/K) on the thermal structure of the oceanic plate is investigated parametrically by comparing the ocean floor depth and heat flux calculated by one-dimensional conduction model with those of GDH1, a theoretical thermal model of the oceanic lithosphere. We find that an optimum fit is obtained, when the value of thermal expansivity is ~3¿10-5, while those associated with the thermal conductivity have many possibilities. The estimates, which give an equally good fit to the GDH1 model, of the plate thickness D (km) and the temperature at the base of the plate Tm(¿C) may be given by Tm~1450-(k0-4.5)¿100-(&agr;-3.0¿10-5)¿105¿100, D~90+(k0-4.5)¿20-(&agr;-3.0¿10-5)¿105¿20 where k0(W/m/K) is the lattice thermal conductivity at the ocean floor. A similar relation is obtained for constant thermal conductivity. ¿ 2001 American Geophysical Union