Oxygen metabolism is uniquely compartmentalized between neurons and glia, the latter comprising about 25% of neuronal energy metabolism. The consumption of acetate and fixation of CO2 in glutamine occur in astrocytes by oxygen-dependent reactions, which power at least two-thirds of astrocyte ATP synthesis. Glia exhibit a large capacity to phosphorylate glucose and can store it in the form of glycogen, the major cerebral energy store, important in providing neuroprotection. Astrocytes can nurture surrounding neurons with substrates such as lactate and glutamine, while at the same time eliminating neurotransmitter glutamate from the synaptic cleft. The metabolic activity of glia can be assessed in vivo using nuclear magnetic resonance spectroscopy.