A number of technologies aimed at detecting oxygen supply/demand imbalance have been developed of which jugular bulb oximetry is the most mature. More recently, near-infrared spectroscopy and direct brain tissue oxygen measurement have become clinically available. The brain extracts oxygen from arterial blood at a rate to supply its global metabolic requirements leaving an oxygen-poor venous effluent. Jugular venous oxygenation can be measured intermittently by serial blood sampling or continuously by fibre-optic oximetry. Jugular bulb oximetry can be used to detect disorders of both cerebral autoregulation and carbon dioxide reactivity. Cerebral oxygenation has been studied by jugular bulb cannulation during aneurysm clipping surgery. Jugular venous saturation has been studied as a potential prognostic marker in comatose patients in which spontaneous circulation has been restored after cardiac arrest. Experience with brain tissue oxygenation microsensors is increasing and clearly these provide a very direct measurement of tissue metabolism.