Oxepin is an oxygen-containing heterocycle consisting of a seven-membered ring with three double bonds.

The parent C6H6O exists as an equilibrium mixture with benzene oxide.

The oxepin–benzene oxide equilibrium is affected by the ring substituents.

[1] A related dimethyl derivative exists mainly as the oxepin isomer, an orange liquid.

[2] Oxepin is an intermediate in the oxidation of benzene by the cytochrome P450 (CYP).