To determine the power loss of hypoid gears often used as axle gears of vehicles a new test procedure has been developed. Hereby the power loss of the test rig can be directly measured using real application conditions. Measurements have shown that axle offset and lubricant have a big influence on the efficiency. Standardized efficiency tests especially for axle gears of passenger cars were worked out to determine the influence of lubricants. Hereby operating points representing common driving cycles are adjusted controled by a computer. These tests have shown that synthetic lubricants can increase the efficiency significantly at high torque.