A pressurizing device and method, for pressurizing a first tank, the device including at least a second tank configured to contain a cryogenic fluid, a first pressurizing circuit for putting the second tank into communication with the first tank, the first pressurizing circuit including at least a first heat exchanger for heating a flow of the cryogenic fluid extracted from the second tank through the first pressurizing circuit, and a second pressurizing circuit with a compressor, branched off from the first pressurizing circuit and leading to the second tank. A feed system for feeding a reaction engine with at least a first liquid propellant includes at least a first tank configured to contain the first liquid propellant, and a device for pressurizing the first tank.