Flow reactor pyrolysis studies of diethyl methylphosphonate (DEMP) in nitrogen have been conducted over the temperature range 802 to 907 K, to gain insight into decomposition mechanisms relevant to incineration of organophosphorus chemical warfare agents. Experiments were conducted in a quartz-lined turbulent flow reactor with residence times between 15 and 125 ms. Two techniques are used to identify products: Fourier-transform infrared (FTIR) spectroscopy for volatile compounds, and gas chromatography/mass spectrometry (GC/MS) preceded by derivatization for products trapped in a liquid-nitrogen bath. Ethylene, ethanol, ethyl methylphosphonate, and methylphosphonic acid were identified as products; ethylene, ethanol and DEMP were quantified using FTIR. The mean ratio of ethylene to ethanol is 1.66. Rates of DEMP decomposition and product formation are independent of loading and reactor diameter. The temperature dependence of the overall DEMP decomposition rate constant was found to be: k[s(-1)]=29 x 10(16) exp(- 59.2 [kcal.mole(-1)]/(R T)). Bond scission and ring transition state mechanisms can explain the formation of ethylene and ethanol from DEMP and ethyl methylphosphonate.