The invention provides methods of cultivating oil-bearing microbes using xylose alone or in combination with other depolymerized cellulosic material. Also provided are microorganisms comprising an exogenous gene encoding a polysaccharide degrading enzyme, such as a cellulase, a hemicellulase, a pectinase, or a driselase. Some methods of microbial fermentation are provided that comprise the use of xylose and depolymerized cellulosic materials for the production of oil-bearing microorgansims.