One future objective for coal-fired generation is to develop advanced ultrasupercritical coal-fired boilers that incorporate oxy-firing to facilitate carbon capture. The steam condition goals of 760°C/34.5 MPa will require major materials changes throughout the boiler including Ni-base alloys in the hottest sections. While a variety of commercial Ni-base alloys are being evaluated in steam and fireside laboratory experiments exposure of model alloys also is needed to understand the roles of alloy additions such as Cr Al Ti Mo and Co in these alloys. Fireside exposures were conducted at 700° and 800°C in simulated oxy-firing conditions for 500h. Alloy additions of Al and Ti were not detrimental to the metal loss under these conditions. However reducing the Cr content from 22% to 18% had a substantial effect. Steam exposures were conducted at 800°C in 17bar steam for up to 5000h. Internal oxidation increased with increasing Ti and Al+ Ti additions similar to observations in commercial alloys._________________________Research sponsored by the Office of Fossil Energy Advanced Research Materials Program U. S. Department of Energy