Pressure regulator/reducer for feeding internal combustion engines with methane characterized in that it consists of: - A body divided into three chambers (2, 3 and 4) each of them having three different inner volumes and wherein chamber has a smaller volume than chamber, and chamber has a smaller volume than chamber; - An adduction methane conduit from tank(s) to chamber through a hole on the wall of chamber; - An on-off valve of the outlet methane from the tank(s); - A connecting conduit of chamber to chamber; - A pressure control valve on the connecting conduit; - A connecting conduit of chamber to chamber; - Adjusting and/or closing devices of the connecting conduit; - A hole of methane passage between chamber and chamber; - A shutter to open and close the hole of the methane passage between chamber and chamber connected to a stem, whose opposite end is integral with an elastic diaphragm; - An elastic diaphragm which separates chamber from chamber, having a proportionally larger surface than the surface of the shutter that opens and closes the hole of the methane passage between chamber and chamber; - An elastic means which cooperates with the methane pressure in chamber in order to keep the shutter sticking to the hole; - A hole in chamber for feeding the methane to the engine. - A pressure sensor placed on the connection to the engine feeding system; - An electronic control unit connected to the pressure sensor and to the adjusting and closing devices of the connecting conduit and to the pressure control valve; - Sealing gaskets; Wherein during the use: - The methane gas pressure within chamber is equal to pressure in the tank(s); - The methane gas pressure within chamber is equal or lower than pressure within chamber; - The methane gas pressure within chamber is equal or higher than pressure within chamber; - The methane gas pressure within chamber is equal to pressure required for the engine feeding. - A body divided into three chambers (2, 3 and 4) each of them having three different inner volumes and wherein chamber has a smaller volume than chamber, and chamber has a smaller volume than chamber; - An adduction methane conduit from tank(s) to chamber through a hole on the wall of chamber; - An on-off valve of the outlet methane from the tank(s); - A connecting conduit of chamber to chamber; - A pressure control valve on the connecting conduit; - A connecting conduit of chamber to chamber; - Adjusting and/or closing devices of the connecting conduit; - A hole of methane passage between chamber and chamber; - A shutter to open and close the hole of the methane passage between chamber and chamber connected to a stem, whose opposite end is integral with an elastic diaphragm; - An elastic diaphragm which separates chamber from chamber, having a proportionally larger surface than the surface of the shutter that opens and closes the hole of the methane passage between chamber and chamber; - An elastic means which cooperates with the methane pressure in chamber in order to keep the shutter sticking to the hole; - A hole in chamber for feeding the methane to the engine. - A pressure sensor placed on the connection to the engine feeding system; - An electronic control unit connected to the pressure sensor and to the adjusting and closing devices of the connecting conduit and to the pressure control valve; - Sealing gaskets; - The methane gas pressure within chamber is equal to pressure in the tank(s); - The methane gas pressure within chamber is equal or lower than pressure within chamber; - The methane gas pressure within chamber is equal or higher than pressure within chamber; - The methane gas pressure within chamber is equal to pressure required for the engine feeding.