In most transmission systems one of themain power loss sources is the loaded gear mesh.High losses there lead to high energy consumption@ high temperatures@ early oil ageing@ increased failure risk and high cooling requirements. In many cases high efficiency is not the main focus and design criteria as load capacity or vibration excitation predominate the gear shape design. Those design criteria mostly counteract highest possible efficiency. The influences of gear geometry parameters on gear efficiency@ load capacity@ and excitation are shown. Thereof design instructions can be derived which lead to low loss gears with equivalent load capacity. According to the designers preference these guidelines can be followed to a varying extent which leads to more or less unconventional@ but more efficient gear design. Low loss gears can save substantial energy in comparison to conventional gears. The power loss reduction is dependent on the operating conditions and can add up to some 70%of the power loss of conventional gears. Such low loss gears have significant advantages in terms of energy consumption@ heat development@ and cooling requirements. For same load carrying capacity and adequate vibration excitation they have@ however@ to be designed with increased centre distance or face width.