A fluid-lubricated gear train, comprising the following features: 1.1 with at least two gearwheels (1, 2) whose teeth mesh with each other; 1.2 with a meshing region which comprises an entrance (4.1) and an exit (4.2); 1.3 with a casing wall which encloses the two mutually cooperating gearwheels and partially or fully blocks off the enclosed interior space against the ambient environment; 1.4 the casing wall comprises an outlet (6.5) in the region of the entrance (4.1) which produces a conductive connection between the interior space and the atmosphere; 1.5 the distance between the tip circle of the gearwheels and the casing wall is smaller than the tooth height, characterized in that 1.6 an overpressure space being provided in the region of the entrance (4.1) and a negative-pressure space being provided in the region of the exit (4.2), and 1.7 the overpressure chamber having a pressure-relief valve, with an external housing being provided with an oil drain (3.1), said housing enclosing the gearwheels (1, 2) and the casing wall, and 1.8 an oil nozzle is provided in the negative-pressure space, so that oil from the oil nozzle is used for lubricating and cooling the gear train, with 1.9 the pressure-relief valve being arranged in such a way that it will open upon exceeding a specific differential pressure between the overpressure space and the remaining interior space enclosed by the external housing, and an oil quantity injected from the oil nozzle will flow through the pressure-relief valve into the interior space of the gear and will leave the interior space of the gear via the oil drain (3.1) in order to be supplied in a circuit to the oil nozzle again. 1.1 with at least two gearwheels (1, 2) whose teeth mesh with each other; 1.2 with a meshing region which comprises an entrance (4.1) and an exit (4.2); 1.3 with a casing wall which encloses the two mutually cooperating gearwheels and partially or fully blocks off the enclosed interior space against the ambient environment; 1.4 the casing wall comprises an outlet (6.5) in the region of the entrance (4.1) which produces a conductive connection between the interior space and the atmosphere; 1.5 the distance between the tip circle of the gearwheels and the casing wall is smaller than the tooth height, characterized in that 1.6 an overpressure space being provided in the region of the entrance (4.1) and a negative-pressure space being provided in the region of the exit (4.2), and 1.7 the overpressure chamber having a pressure-relief valve, with an external housing being provided with an oil drain (3.1), said housing enclosing the gearwheels (1, 2) and the casing wall, and 1.8 an oil nozzle is provided in the negative-pressure space, so that oil from the oil nozzle is used for lubricating and cooling the gear train, with 1.9 the pressure-relief valve being arranged in such a way that it will open upon exceeding a specific differential pressure between the overpressure space and the remaining interior space enclosed by the external housing, and an oil quantity injected from the oil nozzle will flow through the pressure-relief valve into the interior space of the gear and will leave the interior space of the gear via the oil drain (3.1) in order to be supplied in a circuit to the oil nozzle again.