The four chlorinated methanes-methyl chloride, methylene chloride, chloroform, and carbon tetrachloride-were used as models of chlorocarbons with Cl/H ratios of 0.0196 to 0.083 to investigate their thermal stability and hydrodechlorination in excess hydrogen. The reactions were studied in an isothermal tubular reactor at a total pressure of 1 atm with residence times of 0.3-2.0 s between 525 and 900 degrees C. The thermal stability, i.e., the temperature for 99% destruction after 1 s of reaction time was obtained as 875 degrees C for CH3Cl, 780 degrees C for CH2Cl2, 675 degrees C for CHCl3, and 635 degrees C for CCl4. The number and quantities of intermediate chlorinated products decreased with increasing temperature; the formation of nonchlorinated hydrocarbons (CH4, C2H4, and C2H6) increased with temperature. The less chlorinated products were more stable and methyl chloride was the most stable chlorinated methane in these reaction systems. Modeling used a detailed chemical mechanism involving 58 species and 289 elementary reactions; the results are compared with experimental observations. Sensitivity analyses were also performed to rank the significance of each reaction in the mechanism.