An inter-operator radio resource sharing method for sharing radio resources between two or more radio communication systems each controlled by a respective operator and configured to control respective proprietary radio resources and to provide respective served user equipments with radio communication services. The inter-operator radio resource sharing method: determines, by each radio communication system, a bandwidth of respective shared radio resources belonging to the respective proprietary radio resources based on a traffic load related to guaranteed-quality radio communication services requested by the respective served user equipments; signals, by each radio communication system, the respective shared radio resources to other radio communication systems; and provides, by each radio communication system, the respective served user equipments with the radio communication services on the respective proprietary radio resources and on the shared radio resources signalled by other radio communication systems.