The co-oxidative effect of ethanol on methylphosphonic acid (MPA or PO(OH)(2)CH3) was characterized for a range of MPA concentrations (0.1 - 1.0 mM) and ethanol concentrations (0 - 2.4 mM) for temperatures of 473 and 528 degrees C, a pressure of 245 bar, and stoichiometric oxygen for the complete combustion of both organic compounds. Low concentrations of ethanol (0.1 and 0.3 mM) were found to have no statistically significant effect on MPA conversion for an initial MPA concentration of 1.0 mM, but higher concentrations of ethanol caused an increase in the conversion of MPA at T = 473 degrees C, P = 245 bar, and r = 9 s from 14 +/- 2% without ethanol present to 29 2% with 1.0 mM ethanol and 39 +/- 2% with 2.4 mM ethanol. The increase in MPA conversion was more pronounced at shorter residence times. Decreasing the initial concentration of MPA at a constant initial ethanol concentration of 1.0 mM, T = 473 degrees C, P = 245 bar, and r = 9 s resulted in an increase in MPA conversion from 29 2% at 1.0 mM MPA-41 +/- 12% at 0.1 mM MPA. At T = 528 degrees C and P = 245 bar, the initial concentration of MPA had a much greater effect on IVIPA conversion than the initial concentration of ethanol. (c) 2006 Elsevier B.V. All rights reserved.