A fully synthetic transmission/gear oil for both manual gearboxes and in final drives and where an API GL-3, -4 or -5 specification is required being fully compatible with synchromesh gearboxes. The unique formulation not only prevents wear, but also corrosion and foam building are minimized. At high temperatures, the oil is protected against thermal oxidation. Because of the excellent EP characteristics, viscosity drop caused by high loads is minimal, even at prolonged drain intervals.