We report ignition delay time measurements carried out in both constant-volume spray and homogeneous gas phase shock-tube environments at high pressures (1-4 MPa) for 1-decene, trans-5-decene, and n-decane. These measurements provide quantitative kinetic targets for the development of reaction mechanisms and assessment of the relative reactivity of these compounds under low-temperature, negative-temperature-coefficient (NTC), and high-temperature conditions. Derived cetane number (DCN) measurements carried out in spray ignition experiments are shown to be well-correlated with shock tube ignition delay measurements in the NTC region, both of which show substantially reduced oxidative reactivity for the compounds containing double bonds (n-decane versus n-decenes) and lower reactivity for centrally located double bonds (trans-5-decene) compared to a double bond at the end of the carbon chain (1-decene). Ignition delays in both the shock tube and spray show differences of factors of 2-4 for NTC and low-temperature conditions (<900 K) among the three C-10 fuel compounds. At high temperatures (>900 K), shock-tube experiments show a reversal in the reactivity trend, with trans-5-decene being the most reactive and n-decane being the least reactive but with the differences in ignition delay much smaller, of the order of 10-50%.