The major technical obstacle to construction of a 950°C commercial gas-cooled reactor is the absence of a clear basis for the structural design of the metal components. The basis of existing design rules for temperatures to 800°C has been subject to joint U.S. and Federal Republic of Germany review. The result of this review has been used to define complementary structural design programs. Three significant aspects of structural design at 950°C not directly addressed by existing codes have formed a partial basis for work in the United States. These are: design for flaws, for environmental effects, and for a clearly stated definition of reliability. The importance of these three aspects is illustrated, for example, by the fact that component materials, such as the nickel alloys, exhibit markedly reduced toughness below the operating temperature range after elevated temperature exposure. Such materials also display a susceptibility to major mechanical property changes resulting from carbon uptake or loss to the cooling gas. Also there is no satisfactory precedent from which to define design margins. A structural design program is described, some elements of which are being developed.