Relative rate techniques were used to study the reactivity of Cl atoms with a series of ketones in 700 Torr of N-2 or air diluent at 296 K. Rate constants were determined for: butanone, (4.04 +/- 0.33) x 10(-11); 2-pentanone, (1.11 +/- 0.10) x 10(-10); 3-pentanone, ;(8.10 +/- 0.85) x 10(-11); 2-hexanone, (1.88 +/- 0.18) x 10(-10); and 3-hexanone, (1.43 +/- 0.19) x 10(-10) cm(3) molecule' s(-1). The results for 2 and 3-pentanone and 2- and 3-hexanone are approximately a factor of 2-3 greater than reported from recent absolute rate studies. The likely origin of this discrepancy is discussed. (c) 2006 Elsevier B.V. All rights reserved.