A new class of stable aromatic fluids structurally related to the polyphenyl ethers are described. Designated as aromatic C-ethers, they are characterized by resistance to degradation by oxidation, heat, ionizing radiation, and hydrolysis. They are oxidatively stable in the temperature range of 500–600 F and have thermal decomposition temperatures above 700 F. Acceptable damage levels are observed at radiation dosage rates up to 107rads at 375 F. The C-ethers offer considerable promise as high-temperature lubricants with outstanding gear load-carrying capacities. The fluids are compatible with many elastomers and most engineering materials and are essentially nontoxic.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in San Francisco, Calif., October 18–20, 1965.