Materials compatibility studies are being performed in support of the Magma Energy Extraction Project. The behavior of commercially available materials has been examined at magmatic and hydrothermal conditions expected at the Long Valley caldera drill site. Analysis of reaction products reveal that oxidation, and not sulfidation, is the main corrosion problem for most alloys in rhyolite magma, and that reaction with other magmatic components is limited. Metal oxidation was not observed for Cr-bearing alloys in contact with rhyolite glass at hydrothermal temperatures, although these alloys did tarnish in hydrothermal solutions. Consideration of corrosion resistance, high-temperature strength, and cost indicate that Ni-base superalloys offer the most promise for use as construction material of a heat exchanger in rhyolite magma.