Seed triglyceride oils and waxes are high-energy carbon reserves that are utilized by germinating seeds as sources of energy and carbon before the onset of autotrophic growth. The seed oil is sequestered in discrete subcellular organelles termed oil bodies, lipid bodies, or oleosomes. Oil bodies are isolated by centrifugal floatation from seed extracts. This yields a homogeneous preparation of intact oil bodies that can be subjected to further compositional analysis. The spatial distribution of oleosin and oil body accumulation exhibits very different patterns in dicotyledonous and monocotyledonous seeds that may be important in understanding the regulation of the coordinated accumulation of storage substances. Oleosin genes all contain cis-acting elements that respond to abscisic acid and function as positive regulators of gene expression. Much research remains to be accomplished to elucidate the mechanisms of oil body assembly, the regulation of the genes involved, and the process of oil body mobilization.