Theoretical calculations were carried out on the H atom abstraction reaction from methane by XO (X = F, Cl or Pr) radical attack. Geometry optimizations and vibrational frequency calculations were performed using three methods: Moller-Plesset second-order perturbation theory (MP2), quadratic configuration interaction in the space of single and double excitations (QCISD), and the "hybrid" three-parameter exchange functional with Becke's gradient corrected exchange and Lee-Yang-Parr correlation functional (B3LYP). Single-point energy calculations were performed using several high quality basis sets. Canonical transition-stale theory was used to predict the rate constants as a function of temperature (700-2500 K), and three-parameter Arrhenius expressions were obtained by fitting to the computed rate constants. The possible impact of the title reactions in combustion chemistry is also discussed.