A method of producing a synthetic gas (syngas) includes injecting a plurality of reactant streams into a gasification reactor via at least one injection device having a plurality of injection annuli, an inner portion that extends annularly about a centerline extending through the at least one injection device, and an outer portion extending substantially annularly about the inner portion. At least a portion of the outer portion is oriented obliquely with respect to the at least one injection device centerline. The method also includes mixing at least a portion of each of the streams together such that a plurality of recirculation zones is defined by the streams. The method further includes producing a syngas within the recirculation zones via mixing at least a portion of each of the streams. The injection device includes an inner portion that extends annularly about a centerline extending through the injection device. The device also includes an outer portion extending substantially annularly about the inner portion that includes at least one of at least one carbonaceous reactant injection port oriented obliquely with respect to the injection device centerline and at least one outer face oriented obliquely with respect to the injection device centerline.