Jet propellant 10 [(JP-10) or exotetrahydrodicyclopentadiene] is one of the leading candidate fuels for use in pulse detonation engine applications. As such, its ignition delay characteristics have been studied previouslyin very dilute mixtures at pressures from 1 to 9 atm and temperatures from 1300 to 1670 K. The ignition delay times are studied of JP-10/air and JP-10 blended with methylated PCU alkene dimer, nitronorbornane, dinitronorbornane, and ethylhexyl nitrate in air at pressures from 10 to 25 atm and temperatures from 1200 to 2500 K using a shock tube. Ignition delays were primarily measured using CH emission and secondarily using OH emission. Ignition delays were essentially insensitive to all of the additives tested. Additionally, ignition delays for dicyclopentadiene (a suspected intermediate in the combustion of JP-10) were also tested. Above 1500 K, multiple peaks in the CH emission were found. Further tests using OH emission indicate that the main peak in CH emission at these higher temperatures is probably due to reactions involved in the approach to equilibrium and give spuriously long ignition delay times.