Ignition delay times were measured behind reflected shock waves for cyclohexane, methylcyclohexane, and n-butylcyclohexane at 1.5 and 3 atm, equivalence ratios near 1 and 0.5, and temperatures between 1280 and 1480 K. The observed ignition delay times can be summarized as follows: methylcyclohexane > n-butylcyclohexane cyclohexane. Several reasons are suggested to explain the ordering of the ignition delay times for these three naphthenes. We believe that this work provides the first set of ignition delay time data for n-butylcyclohexane. In addition, H2O and OH time-histories were recorded during the oxidation of cyclohexane, methylcyclohexane, n-butylcyclohexane, iso-octane and n-heptane under similar test conditions. OH time-histories near time zero are distinctive for each type of fuel studied, and these early-time OH profiles provides critical insight into the influence of molecular structures on ignition behavior, particularly in the case of the cycloalkanes. Comparisons of measured time-histories with simulations from recent cycloalkane oxidation mechanisms are also presented. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.