Products of the gas-phase reactions of OH radicals with O,O-diethyl methylphosphonothioate [(C2H5O)(2)P(S)CH3, DEMPT] and O,O,O-triethyl phosphorothioate [(C2H5O)(3)PS, TEPT] have been investigated at room temperature and atmospheric pressure of air using in situ atmospheric pressure ionization mass spectrometry (API-MS) and, for the TEPT reaction, gas chromatography and in situ Fourier transform infrared (FT-IR) spectroscopy. Combined with products quantified previously by gas chromatography, the products observed were: from the DEMPT reaction, (C2H5O)(2)P(O)CH3 (21 +/- 4% yield) and C2H5OP(S)(CH3)OH or C2H5OP(O)(CH3)SH (presumed to be C2H5OP(O)(CH3)SH by analogy with the TEPT reaction); and from the TEPT reaction, (C2H5O)(3)PO (54-62% yield), SO2 (67 +/- 10% yield), CH3CHO (22-40% yield) and, tentatively, (C2H5O)(2)P(O)SH. The FT-IR analyses showed that the formation yields of HCHO, CO, CO2, peroxyacetyl nitrate [CH3C(O)OONO2], organic nitrates, and acetates from the TEPT reaction were < 5%, 3 +/- 1%, < 7%, < 2%, 5 +/- 3%, and 3 +/- 2%, respectively. Possible reaction mechanisms are discussed.