A fuel conditioning method is applicable to common rail direct injection or unit injector system. A liquid fuel is conditioned for higher-efficiency combustion in a combustion chamber. The conditioning system includes a fuel vessel for fuel conditioning, at least one fuel dispersing nozzle mounted for discharge into the fuel conditioning vessel, at least one gas inlet port, and at least one conditioned fuel outlet port located in the vessel. A gas source feeds a gas to the fuel conditioning vessel, wherein the gas is dissolved in the liquid fuel for forming a liquid/gas fuel solution. A low-pressure fuel pump and a liquid fuel supply line deliver liquid fuel from a fuel tank to the at least one dispersing nozzle of the fuel vessel at pressure P.sub.1 higher than the gas pressure P.sub.2. A high-pressure fuel pump feeds the liquid fuel/gas solution into a common rail and further into fuel injectors, providing a pressure P.sub.4 higher than a pressure P.sub.5 in the combustion chamber at a moment of combustion.