An improved conveyor oven for cooking food products more efficiently is provided. The delivery system for hot convection currents includes a lower delivery system using tapered slot nozzles which are mutually spaced along the length of travel of the conveyor and extend laterally thereto. The upper heat delivery system utilizes an upper plenum with openings in the lower surface thereof which coincides with the upper surface of the heating chamber. The openings are initially in a first plate, rectangular mutually-spaced openings which extend both laterally and the length of the path of travel of the conveyor. Beneath the rectangular openings tapered slots are provided in registry therewith which extend laterally across the path of travel of the conveyor and open away from the entrance to the upper plenum for the heated air. The slots terminate in depending flanges which also extend substantially laterally to the path of travel of the conveyor and are angled outwardly whereby heated air is focused downwardly and laterally across the path of travel of the conveyor, but not parallel thereto. Finally, if desired, the heated air at the entrance to the conveyor may be further restricted by perforated strips overlying the rectangular openings to further reduce said openings.