A hyperbaric fuel system (10a, 10b) produces hydrogenated liquid fuel (30) for combustion reactions of compression or spark ignition engines and improves fossil fuel efficiency without requiring major changes to existing fuel systems. The hydrogenated liquid fuel (30) decreases the NOx, CO and unburned hydrocarbon particulate matter, and reduces the consumption of liquid fuel (26). The systems produces hydrogen gas (18) and dissolves the hydrogen gas (18) in the liquid fuel (26) using several chambers, including a hyperbaric mixing chamber (58), between the liquid fuel supply and a fuel pump (28) supplying the hydrogenated liquid fuel (30) to fuel injectors (40). Unused hydrogen gas (18) and hydrogenated liquid fuel (30) is recirculated to minimize loss of efficiency. The system preferably includes a water reservoir and electrolysis device to generate the hydrogen gas.