This paper presents an experimental study that focuses on the formation of perfluoroisobutene (i-C4F8). Experiments were carried out at atmospheric pressure in a quartz flow tube reactor over the temperature range of 823 to 1273 K and an initial reactant feed concentration of 2% with the balance nitrogen. Reactants studied include chlorodifluoromethane (CHF2Cl), 1,1,1,2-tetrafluoro-2-chloroethane (CF3CHFCl), trifluoromethane (CHF3), perfluoropropene (C3F6), and mixtures of these species. Effluent gas concentrations were obtained using a water cooled gas sampling probe, and analysis of products was performed via on line gas chromatography with flame ionization detection and gas chromatography with mass selective detection. C3F6 pyrolysis produced more than 22% i-C4F8 yield, while mixtures with CHF2Cl and CHF3 resulted in i-C4F8 yields of 14% and 28%, respectively. The pyrolysis of CF3CHFCl resulted in slightly greater than 6% i-C4F8 yield, and (CHFCl)-Cl-2 decomposition produced up to 6% i-C4F8 yield, while CHF2Cl/CF3CHFCl copyrolysis produced 8% yield of i-C4F8. These results show that the addition of a difluoromethylene ((1):CF2) source increases i-C4F8 production. This suggests that a major pathway to i-C4F8 production may be C3F6 isomerization to singlet perfluorodimethylcarbene ((1):C(CF3)(2) and subsequent collisional stabilization to the tripler carbene ((3):C(CF3)(2)) followed by either (1):CF2 addition or further reaction with C3F6. This work focuses on an experimental study. Detailed modeling work is ongoing.