Mean Time Between Failures (MTBF) became a frequently used value describing reliability of components@ assemblies@ and systems. While MTBF was originally introduced and used mainly in conjunction with electronic components and systems@ the definition and application for mechanical components@ such as gearboxes@ is not broadly available@ used@ or recognized. In the field of gears it is difficult to obtain an MTBF from the manufacturer due to the lack of applicable@ generally recognized definitions and standards. The paper will evaluate@ compare and suggest ways in determining a gearbox MTBF based on the already established@ proven@ design calculation standards and test methods used in the gear design.