Abstract: An apparatus and a method of saturating liquid fuel with air, oxygen, or another gas for injecting into an internal combustion engine. The internal combustion engine is provided with a gas compressor or pump for compressing air or oxygen, which is directed into a fuel saturator having a dense, porous material or stone therein and having a liquid hydrocarbon fuel being fed therethrough. Compressed gas is fed onto one side of the stone and is forced therethrough for saturation into the liquid fuel, which is then fed into a fuel injection system of an internal combustion engine. Gas that separates from the liquid fuel is trapped and vapor is removed therefrom. The fuel saturator uses a gas saturation stone, which may be hollow in one end for feeding a compressed gas thereinto, while the other side is surrounded with the liquid hydrocarbon fuel. The liquid hydrocarbon fuel may be fed around a spiralling passageway adjacent the stone for a more complete saturation of the fuel.