The thermal decomposition of CH3ONO was studied in a static reactor at temperatures in the range 450-520 K. Stable products were analyzed by FTIR and gas-liquid chromatography to yield concentration-time profiles as functions of temperature and pressure. The species monitored included CH3ONO, CH2O, CH3OH, NO, N2O, and CO. The experimental data were kinetically modeled with the aid of Rice-Ramsperger-Kassel-Marcus (RRKM) calculations for pressure-dependent rate constants. The key reactions of this mechanism are the following: CH3ONO → CH3O + NO (1); CH3ONO → CH2O + HNO (2); CH3O + NO → CH3ONO (3); CH3O + NO → CH2O + HNO (4); CH3O + HNO → CH3OH + NO (5); HNO + HNO → N2O + H2O (7). The results showed that the initiation reaction, (1), is clearly pressure-dependent in the temperature and pressure ranges investigated. The data are consistent with the value k1 = 1015.3±0.30 exp((-38 700 ± 400)/RT) s-1 at 710 Torr of He and with the extrapolated high-pressure rate constant k1 ∞ = 1016.01±0.30 exp((-39600 ± 400)/RT) s-1. The rate constant ratio k4/k3 for channels 3 and 4 was also found to depend on both temperature and pressure. At 710 Torr, k3 = 1012.96±0.30 exp((0 ± 200)/RT) and k4 = 1012.92±0.30 exp((-2050 ± 200)/RT), both in units of cm3/(mol s) Kinetic modeling of CH3OH and N2O formation over the entire range of temperatures and pressures investigated here yielded k5 = 1013.5±0.4 exp((0 ± 400)/RT) and k7 = 108.93±0.30 exp((-3100 ± 300)/RT) cm3/(mol s).