For better efficiency in transmissions, lower viscosity grades of gear oils and reduced oil volumes are often used. With increasing power density and extended oil drain intervals, the demands on the lubricant as a design element increase accordingly. The introduction of lubricant properties in load-carrying capacity rating requires not only knowledge of their physical properties such as viscosity, viscosity-temperature, or viscosity-pressure behavior, but also the quantitative influence of the performance additive on scuffing, wear, micropitting, and pitting of gears.