A method and an installation for loading and unloading compressed natural gas on ships, said ships being suitable for sea navigation and the ships having receivers. The compressed natural gas is storable in tubes, installed on the receivers. The installation comprises fixed containers for housing tubes, supports for holding a container supported above the sea surface at a given height, devices operable for lowering the receivers, such as to carry each receiver below a fixed container and to lift the receivers so as to lift the fixed container above the given height to support the containers on the receivers.