Fuel generating machine’s working mechanism is to convert hydraulic energy into mechanical energy which can easily be converted in other more useful forms such as electrical energy and thermal energy while generating more energy than an input. Using principles of buoyancy and weight variance, machine can generate more energy than input and hence is an efficient energy/fuel generating machine. Technology can be employed in machines with different configurations, some using a fuel generating tube working according to such techniques. This invention can lead to pollution free, renewable and highly efficient energy sources that produce energy for domestic uses as well as for other uses such as vehicles and industries. This invention does not require complex and capital intensive infrastructure.