The Sate coefficient for the reaction O + ClO --> Cl + O-2 (1) was measured over the range 227 to 362 K using a discharge flow tube coupled to a pulsed laser photolysis-atomic resonance fluorescence apparatus. The title reaction was studied under pseudo-first-order conditions in O atoms in an excess of ClO. ClO radicals were produced in the discharge flow tube by the reaction of Cl with either O-3 or Cl2O and its concentration was measured in situ by UV absorption. O atoms were produced by pulsed laser photolysis of ClO at 308 nm and detected by atomic resonance fluorescence. The measurements yield k(1)(T) = (3.0 +/- 0.8) x 10(-11) exp((75 +/- 40)/T) cm(3) molecule(-1) s(-1), where the uncertainties are at the 95% confidence level and include estimated systematic errors. These results are compared with previous data and an expression that can be used for atmospheric purposes is suggested.