To better understand the long-term elevated temperature performance of reinforced flexible graphite sheet gaskets installed in a bolted flanged joint, a Pressure Vessel Research Council (PVRC)-sponsored program was launched in 1991 and was extended in 1992-1993 by the participation of a private gasket manufacturer company (Polycarbon, Inc.). The elevated temperature behavior of these gasket materials with and without different types of metallic reinforcement and/or passivating corrosion and oxidation inhibitor has been evaluated according to specific room and elevated test procedures. Their long-term elevated temperature joint behavior has been estimated on the basis of Material Technology Institute of the Chemical Process Industries (MTI)PVRC gasket quantification tools developed in 1986-1987 essentially for elastomeric fiber-reinforced sheet gasket materials and extended to flexible graphite gasketing products.This report presents a summary of the test results obtained and the development of quantification tools for flexible graphite sheet materials that permits the assessment of their probable long-term performance in service in a joint.