As part of a search for more thermostable supports for combustion catalysts for gas turbine applications, a series of complex oxide materials were prepared by sol-gel synthesis and two different coprecipitation routes. The materials were chosen on the basis of literature studies; two hexaaluminates (LaAl11O18 and BaMnAl11O19-alpha), a perovskite (SrZrO3), a spinel (MgAl2O4), and a pyrochlore (La2Zr2O7). After synthesis, the materials were aged for 16 h in a flow of humid air at temperatures between 1100 and 1400 degrees C, simulating the actual conditions in a catalytic combustor. The aged samples were characterized by X-ray diffraction, nitrogen adsorption for determination of BET surface area, and scanning electron microscopy. The sol-gel materials generally exhibited higher thermal stability than their coprecipitated counterparts. One exception was LaAl11O18, which had the highest surface area of all materials, 8 m(2)/g, after aging at 1400 degrees C, both for the sol-gel synthesized and one coprecipitated material. The reaction paths for the high-temperature solid-state reactions depended on preparation procedure and stoichiometry of the product.