Vehicles fueled by liquefied petroleum gas (LPG) are also required to provide high levels of engine torque and power, in addition to clean emissions for environmental friendliness, low fuel consumption and energy savings. In response to these demands, it can be expected that engine control performance and exhaust emissions can be substantially improved by controlling the fuel supply system with high accuracy. Energy savings along with higher levels of speed, accuracy and reliability can also be expected. The conventional method of controlling fuel supply systems has been to control the fuel injection pressure to a high level at all times under all engine operating conditions, regardless of the amount of fuel injected. However, in order to keep the fuel injection pressure at a constant level under all engine operating conditions, the fuel pump drive motor has to operate at a higher speed when an exceptionally large amount of fuel is injected from the injector such as under high engine loads. That requires the application of a large current to the pump drive motor, resulting in the deterioration of fuel economy. In addition, applying a large current to the drive motor over a long period of time raises the temperature of the motor, motor drive mechanism and the fuel pump itself, thereby affecting their durability. Another drawback is that it also affects the temperature of the fuel discharged from the fuel pump. This paper proposes a method for substantially reducing the energy consumption of a liquid LPG injection system during high-speed engine operation. The proposed method focuses on the fact that the fuel injection pressure need not be set high if there is little likelihood of the fuel vaporizing such as when a large quantity of fuel is injected. On the other hand, the injection pressure must be set high if the fuel is apt to vaporize such as when an exceptionally small amount of fuel is injected. However, it must be noted that varying the fuel injection pressure requires correction of the operating characteristics of the injector and other components. The proposed method provides variable control of the target fuel injection pressure. Specifically, the target fuel injection pressure is determined and controlled according to the fuel injection quantity, which varies depending on the engine operating speed. Because this variable control method allows the target injection pressure to be set low at times of high engine output, the current applied to the fuel pump drive motor can be markedly reduced compared with the conventional control procedure. As a result, energy consumption by the drive motor is reduced, which has the effect of improving fuel economy. In addition, the proposed method also improves the durability of the motor, motor drive mechanism and fuel pump. The effectiveness of this proposed control method has been confirmed by simulations and verification tests.