The power source is a design characteristic for a mobile robot in which the energy source used must provide enough power for a desired period of time depending on the specific task of a robot. Batteries are the most common power source of energy on mobile robots. Important factors for selecting battery solution as the power source includes weight of the batteries, maximum power availablility, maximum discharge rate, and the endurance of a battery. On the other hand, when the ratio of weight to energy is considered, overall, a gasoline engine is more efficient than a battery power system. This paper explains a design and realization of a hybrid energy system for a mobile robot where a gasoline engine powers an alternator to create electricity and this electrical energy is used to drive and power the electronics of the robot, with the understanding that it can only be used outside. The theory of a gasoline-electrical hybrid power system is explained and later by using a 5.5 horsepower (hp) Loncin engine and a car alternator a hybrid system is designed, manufactured and tested. The test results show the effectiveness of the design.