The production of microbial oil is an aerobic process that can be modeled as the sum of three stoichiometric reactions: oil production from sugar, respiration, and cell growth. The aerobic fermenter is assumed to have a high heat-production rate of 110 kcal per mol of O2 consumed, consistent with published literature. The nitrogen present is a complex mixture of nucleic acids, protein, and other reduced forms of nitrogen; as such, the conversion of these components to cell mass is neglected. Magnesium sulfate is provided in the bioreactor model to provide Mg and S to support cell growth. These are also excluded from the growth reaction because the Mg and S contribution to the cell mass is minimal. Any substrate not converted to cell mass or oil is assumed to be consumed for respiration. Given the yield of TAG, Yp (g•g -1 ), and the fraction of biomass produced over the total substrate not consumed for oil production (Yb; g•g -1 ), the extent of reaction for TAG production (Xp), growth (Xb), and respiration (Xr), can be calculated (Table ).