The room-temperature reactions of the chemical warfare agents VX (O-ethyl S-2-(diisopropylamino)ethyl methylphosphonothioate), GD (3,3-dimethyl-2-butyl methylphosphonofluoridate, or Soman), and HD (2,2＇-dichloroethyl sulfide, or mustard) with nanosize MgO have been studied using solid-state MAS NMR. All three agents hydrolyze on the surface of the very reactive MgO nanoparticles. VX yields ethyl methylphosphonic acid (EMPA) and methylphosphonic acid (MPA), but no toxic S-(2-diisopropylamino)ethyl methylphosphonothioate (EA-2192). GD forms both GD-acid and MPA. For HD, in addition to hydrolysis to thiodiglycol, about 50% elimination to divinyl sulfide occurs. The reaction kinetics for all three agents are characterized by a fast initial reaction followed by gradual slowing to a steady-state reaction with first-order behavior. The fast reaction is consistent with Liquid spreading through the porous nanoparticle aggregates. The steady-state reaction is identified as a gas-phase reaction, mediated by evaporation, once the liquid achieves its volume in the smallest available pores.