An experimental study of the pyrolytic behavior and thermal reactions of 2-chloro-1,1,1,2-tetrafluoroethane(HCFC-124) has been conducted over the temperature range 923 to 1048 K and atmospheric pressure. A tubular reactor was fed mixtures diluted to 2% HCFC-124 by volume with a helium or hydrogen balance. Results were obtained using a water-cooled gas sampling probe with on-line GC/MS and GC/FID analysis for stable product identification and reactant and stable product quantification. Products of the decomposition in helium include C3F6 (major product), C2F4, CFCl2CF3, the cis and trans isomers of perfluoro-2-butene, and isoC(4)F(8). Products observed in hydrogen include CH2FCF3 (major product), CH2F2, CHF3, CH3F, CF3CH3, and CHF2CHF2. The addition of hydrogen was observed to greatly increase reactant conversion and shift product selectivities away from perfluorinated olefins and chlorinated species. A QRRK analysis of reactant decomposition is presented and discussed; HCFC-124 appears to decompose primarily by alpha,alpha-HCl elimination to form singlet perfluoromethylcarbene ((1):CFCF3) with carbon-chlorine bond rupture competing at higher temperatures. Also presented is a QRRK analysis on the (1): CFCF3 <----> C2F4 1,2-F migration isomerization. This isomerization as a major pathway toward C3F6 formation in helium is consistent with experimental observations. C3F6/C2F4 product selectivity observed in helium is consistent with a high activation energy for the isomerization (36 kcal/mole) and a low (1):CF2 heat of formation (-44 kcal/mole).