This paper will discuss the unique properties of Therban AT, a portfolio of low Mooney viscosity hydrogenated nitrile butadiene rubber grades. These grades have unprecedented low Mooney viscosity (ML1+4 at 100°C about 39) combined with a narrower molecular weight distribution which provides optimum mechanical properties. These grades offer all of the advantages of regular HNBR while providing improved processing characteristics, such as easier mixing, faster injection molding cycles, faster extrusion rates and smoother surfaces/edges of extruded parts without the need for processing aids. The paper will present the physical properties as well as oil and fuel aging data of low Mooney viscosity HNBR polymers with high acrylonitrile content formulated in black and mineral-filled recipes and cured by peroxide or sulfur.