The gas phase reactions of iodine atoms with ethane, propane, isobutane and normal butane have been studied in a high vacuum system of conventional design. The apparatus was constructed of pyrex glass and the section used for handling iodine was fitted with greaseless metal valves and maintained at 120°C in a heated box. Product analysis was by gas liquid and gas solid chromatography. The mechanism assumed for the reactions mentioned above is described by reactions one to six written below. Absolute values for k2, the rate constant of reaction 2, have been measured for ethane, propane and isobutane and the Arrhenius parameters for these reactions calculated. The activation energies combined with accurate estimates for that of reaction 4 have been used to calculate the endothermicity of reaction 2 and these reaction heats combined with knowledge of the bond dissociation energy of HI have led to values for the C--H bond dissociation energies in ethane, the secondary position in propane and the tertiary position in isobutane. The data for the Arrhenius parameters of reaction 2 and. the C-H bond dissociation energies are tabulated below. Other related thermochemical data has been calculated from these bond strength values.