Gas distribution system for feeding to an engine powered by alternative gas fuel, gas contained in a first gas tank and at least in a second gas tank, said system having a first gas conduit connecting an output of the first gas tank and a second gas conduit connecting an output of the second gas tank, wherein valve means (7,8) are provided on the conduits (12,14) to select the gas tank (3,4) having the highest gas pressure and suppling to the engine the gas provided by the selected tank; said valve means further comprise at least first check valve that is interposed in the first gas conduit and a second check valve that is interposed in the second gas conduit so that the first and the second valves (21, 22) are placed on opposite sides of a merge point where the first conduit and the second conduit meet and may be opened by the difference of pressure of the gas in the first/the second gas conduit (12 e 14) and the merge point; a supply gas conduit connects the merge point and a pressure regulator supplying the gas to the engine; the supply gas conduit contains the gas originated by the gas tank (3, 4) having the highest pressure; the gas distribution system is characterized in further comprising a gas recharge conduit that has one free end (24-a) provided with a check-valve and another end (24-b) that bifurcates in a first branch that is connected with the first gas conduit in a position between the first check valve and the first gas tank and a second branch that is connected with the second gas conduit in a position between the second check valve and the second gas tank; the first branch is provided with a third check valve that is opened when pressurized gas is supplied to the gas recharge conduit; the second branch is provided with a fourth check valve that is opened when pressurized gas is supplied to the gas recharge conduit. said valve means further comprise at least first check valve that is interposed in the first gas conduit and a second check valve that is interposed in the second gas conduit so that the first and the second valves (21, 22) are placed on opposite sides of a merge point where the first conduit and the second conduit meet and may be opened by the difference of pressure of the gas in the first/the second gas conduit (12 e 14) and the merge point; a supply gas conduit connects the merge point and a pressure regulator supplying the gas to the engine; the supply gas conduit contains the gas originated by the gas tank (3, 4) having the highest pressure; the gas distribution system is characterized in further comprising a gas recharge conduit that has one free end (24-a) provided with a check-valve and another end (24-b) that bifurcates in a first branch that is connected with the first gas conduit in a position between the first check valve and the first gas tank and a second branch that is connected with the second gas conduit in a position between the second check valve and the second gas tank; the first branch is provided with a third check valve that is opened when pressurized gas is supplied to the gas recharge conduit; the second branch is provided with a fourth check valve that is opened when pressurized gas is supplied to the gas recharge conduit.