The net amounts of ATP generated by glycolysis depend on whether the process is occurring anaerobically or aerobically. Under aerobic conditions, the citric acid cycle, the electron transport system (ETS) and oxidative phosphorylation (OxPhos) are all occurring too. When this happens all of the carbons in glucose can ultimately be oxidized to CO2 and the total yield is 38 molecules of ATP per molecule of glucose. Under anaerobic conditions, only two molecules of ATP are produced per molecule of glucose. If the citric acid cycle is not occurring, but ETS and OxPhos are, 8 molecules of ATP are produced per molecule of glucose.