Derived values of the thickness of the effective elastic lithosphere on Mars are converted to estimates of lithospheric thermal gradients and surface heat flow by finding the thickness of the elastic-plastic plate having the same bending moment and curvature, subject to assumed strain rates and temperature-dependent flow laws for crustal and mantle material. Local thermal gradients and heat flow values so estimated were 10--14 K km-1 and 25--35 mW m-2, respectively, at the time of formation of flexurally induced graben surrounding the Tharsis Montes and Alba Patera, while gradients and heat flow values of less than 5--6 K km-1 and 17--24 mW m-2, respectively, characterized the lithosphere beneath the Isidis mascon and Olympus Mons at the time of emplacement of these loads. On the basis of the mean global thickness of the elastic lithosphere inferred to support the Tharsis rise and estimates of mantle heat production obtained from SNC meteorites, it is suggested that the present average global heat flux on Mars is in the range 15--25 mW m-2. Approximately 3--5% of this heat flux during the Anazonian epoch has been contributed by excess conducted heat in the central regions of major volcanic provinces. Most likely, this excess heat flux has been delivered to the base of the lithosphere by mantle plumes. The fractional mantle heat transport contributed by plumes during the last 2 b.y. on Mars is therefore similar to that at present on Earth. ¿ American Geophysical Union 1990