With continuous demand for energy, it is apparent that the world's current fuel and energy source is limited. Burgeoning attempts at cellulose and hemicellulose utilization for efficient biofuel production is a common endeavor amongst scientists, yet the metabolic boundaries within Saccharomyces cerevisiae, as well as laboratory limitations, has proven to be challenging. It is necessary to engineer multiple genes in several different combinations or genetic backgrounds in order to obtain efficient fermentation. This is a major technical challenge using traditional approaches. Recombineering is a promising in vivo multi-gene cloning method for organisms, such as Saccharomyces cerevisiae, that are especially susceptible to DNA repair via homologous recombination because it overcomes several shortcomings with traditional amplification-ligation cloning techniques. Using a previously engineered plasmid containing native xylose-degradation genes from the yeast Pichia stipitis, pSDM20, a new plasmid designated pMA300.4.3 was genetically recombineered to harbor two additional Pichia stipitis genes, transketolase and transaldolase, and thereby improve Saccharomyces cerevisiae's fermentative capabilities on xylose by increasing activity within the pentose phosphate pathway. Recombineering within Saccharomyces cerevisiae was especially beneficial because it was time-efficient and gave successful in vivo plasmid construction when there were a limited number of restriction enzyme digest sites available. Thus, recombineering proved to be a stable and effective means of plasmid construction in vivo and genetic manipulation in attempts at improving the fermentative capabilities of Saccharomyces cerevisiae.