A fuel system for an internal combustion engine comprising - a first fuel container for a first fuel, a second fuel container for a second fuel, a pump , and a first fuel injector , the fuel system being arranged to provide a communication between the first fuel container and the pump and between the pump and the first fuel injector , - wherein the fuel system further comprises a reservoir with a separation device adapted to divide the reservoir into a first volume and a second volume , whereby the separation device may be moved or flexed by a pressure difference in the first and second volumes so as to change the sizes of the first and second volumes , - wherein the fuel system is arranged to provide a communication between the pump and the first volume , and to provide a communication between the second fuel container and the second volume and between the second volume and a second fuel injector , whereby the fuel system provides for a single fuel pump being used for delivering two fuels of different types to a cylinder of the engine, - characterized in that said reservoir, separation device, first volume and second volume are a primary reservoir , a primary separation device , a primary first volume and a primary second volume , respectively, the fuel system also comprising a secondary reservoir with a secondary separation device adapted to divide the secondary reservoir into a secondary first volume and a secondary second volume , whereby the secondary separation device may be moved or flexed by a pressure difference in the secondary first and second volumes so as to change the sizes of the secondary first and second volumes , wherein the fuel system is arranged to provide a communication between the pump and the secondary first volume , and to provide a communication between the second fuel container and the secondary second volume and between the secondary second volume and the second fuel injector . - a first fuel container for a first fuel, a second fuel container for a second fuel, a pump , and a first fuel injector , the fuel system being arranged to provide a communication between the first fuel container and the pump and between the pump and the first fuel injector , - wherein the fuel system further comprises a reservoir with a separation device adapted to divide the reservoir into a first volume and a second volume , whereby the separation device may be moved or flexed by a pressure difference in the first and second volumes so as to change the sizes of the first and second volumes , - wherein the fuel system is arranged to provide a communication between the pump and the first volume , and to provide a communication between the second fuel container and the second volume and between the second volume and a second fuel injector , whereby the fuel system provides for a single fuel pump being used for delivering two fuels of different types to a cylinder of the engine, - characterized in that said reservoir, separation device, first volume and second volume are a primary reservoir , a primary separation device , a primary first volume and a primary second volume , respectively, the fuel system also comprising a secondary reservoir with a secondary separation device adapted to divide the secondary reservoir into a secondary first volume and a secondary second volume , whereby the secondary separation device may be moved or flexed by a pressure difference in the secondary first and second volumes so as to change the sizes of the secondary first and second volumes , wherein the fuel system is arranged to provide a communication between the pump and the secondary first volume , and to provide a communication between the second fuel container and the secondary second volume and between the secondary second volume and the second fuel injector . <EOS>