Feedstock delivery systems for hydrogen generation assemblies having a hydrogen-producing region and a heating assembly. The delivery system provides a hydrogen-production fluid to the hydrogen-producing region and provides a heating fuel to the heating assembly. The delivery system includes a pressure vessel having an interior cavity containing the heating fuel and the hydrogen-production fluid, which are disposed in the pressure vessel in a pressurizing--pressurized relationship, in which the heating fuel is discharged from the pressure vessel under it own pressure and the hydrogen-production fluid is discharged under pressure applied by the heating fuel. The feedstock delivery system may separately discharge the hydrogen-production fluid and the heating fuel and may include a pressure transmitter disposed between the hydrogen-production fluid and the heating fuel. The heating fuel may be a condensable fluid and the hydrogen-production fluid may be a liquid at the operating conditions of the feedstock delivery system.