An improved fuel efficient commercial LP-Gas burner/canteen burner is disclosed, wherein a gas nozzle is fitted into an outer threaded tube, which is in turn fitted onto onn end of a mixing head having circumferential primary air opening. The improvement is characterized in the said mixing head being provided at the other end with a convergent-divergent mixing tube capable of providing a venturi effect. The convergent portion being towards the mixing head and the divergent portion being provided with a gas-air burner base consisting of a bottom closed concentric double walled mixing chamber having gas-air mixing space and a central secondary annular opening for air. The said concentric double walled mixing chamber being provided with a removably fixed annular-ring burner head having perforated inner and outer tapered edges. The said burner head being provided with a removably fixed annular ring shaped spill tray with circular tertiary air opening. The convergent-divergent mixing tube providing a venturi effect at the initial gas-air mixing stage coupled with the tertiary air opening provided by the annular ring shaped spill tray at the burner head results in improvement of the thermal efficiency, resulting in the direct saving of fuel.