An improved vehicle fuel system enables mixing of natural gas and a liquid fuel upstream of a combustion cylinder. According to some embodiments the system includes: a gas pressure vessel and associated gas pressurization system to deliver natural gas at a desired pressure; a liquid fuel storage vessel and associated reservoir pump to deliver liquid fuel at a desired pressure; a mixing system configured to receive and mix the liquid fuel from the liquid fuel storage vessel and natural gas from the gas pressure vessel to produce a homogeneous fluid fuel mixture; and a common rail system connecting the mixing system to an engine that consumes the homogeneous fluid fuel.