Recently introduced perfluorinated polyether rubbers have been found to be useful materials for use as o-rings in harsh environments. They have a very broad range of thermal utility, -55 degrees C to 200 degrees C, and exhibit strong resistance to harsh chemical environments over the entire temperature range. The data presented here demonstrate the excellent high and low temperature performance of perfluorinated polyether rubbers after extended exposures to jet fuel and synthetic hydraulic fluids. Demonstration of an appreciable degree of retained sealing force by molded o-rings down to -40 degrees C is shown in a compression stress relaxation device. Perfluorinated polyether o-rings are demonstrated to offer significant improvement in performance over current nitrile-based o-ring materials.