Supercritical fluids have been the subject of much recent interest as solvents in which to study fundamental photochemical reactions, since they allow, through changes in pressure and temperature, changes in a number of solvent parameters without changing chemical identity. As a result it is possible to control or tune a reaction by adjusting temperature and/or pressure. Ground state molecular oxygen (3Σg-) is a potent quencher of electronically excited states of molecules. Transient absorption of triplet benzophenone (3BP) has been studied as a function of temperature and pressure, to investigate the reactivity of triplet benzophenone toward molecular oxygen, in supercritical carbon dioxide. The spin statistical factors suggests a maximum of 4/9 possible pathways result in quenching for two triplets, proceeding either via energy transfer to molecular oxygen (1/9) or via intersystem crossing to the ground state (3/9).