Results are presented of the measurements of the thermal resistance of dry and oil-filled joints formed between two flat surfaces of various metals. Experimental apparatus consisted of two test blocks, 3 in. diam × 3 in. long, stacked axially on one another, in contact with an inductively heated copper block at one end and with a water-cooled copper block at the other, all placed between the platens of a hydraulic press. The thermal conductance of the joint formed between the two test blocks was obtained from the measured heat flow and temperature gradient through the blocks and studied as a function of temperature, pressure, and surface finish. The temperature at the joint ranged from 300 to 500 F, the thermal current across the joint from 10,000 to 130,000 Btu/(hr) (sq ft), the temperature drop across the joint from 1 to 100 F, and the pressure on the joint from 2 to 8000 psi. The thermal resistance, interpreted by analogy to the concept of electrical spreading resistance, is decreased by increasing the temperature and pressure, by the inclusion of oil, or by plating the surfaces with a soft metal.