Abstract The electrochemical behavior and electrogenerated chemiluminescence (ECL) of bis(2,4,6-trichloro-phenyl) oxalate (TCPO) in acetonitrile+benzene (2:1 v/v) solutions have been investigated. Quasireversible one-electron reduction of TCPO occurs, and the reduction product, the anion radical TCPO − (in the absence of O 2), is stable on the cyclic voltammetric time scale. In the presence of oxygen, TCPO − and O − 2 react, ultimately producing trichlorophenoxide ion and CO 2. ECL is observed on reduction of TCPO+O 2 solutions containing a luminescent compound (e.g., 9,10-diphenylanthracene) where the ECL spectrum is typical of the luminescer. No ECL is observed in the absence of O 2 during reduction of TCPO and fluorescer. The ECL only appears with trace amounts of O 2, suggesting that this system might be useful as a detector for very low concentrations of O 2.