Detonation velocities and limits for the system perfluorocyclobutane-fluorine have been measured. The velocities have been compared with computed Chapman-Jouguet velocities. This is, so far as we know, the first time a systematic study has been made of the combustion of a fluorocarbon with fluorine. Adiabatic flame temperatures and compositions for this system are computed and reported. It is shown that, with simple systems such as these, detonation velocity measurements can be used to compute standard enthalpies of formation with a precision comparable to that of calorimetric measurements. A solid state optical sensor was used to detect the passage of the detonation wave in a stainless steel detonation tube.