The acid dissociation constants (pK(a)) of four organic acids (formic, acetic, propanoic, and butanoic) commonly found in monoethylene glycol (MEG) regeneration systems and methyldiethanolamine (MDEA) were measured via potentiometric titration. Dissociation constants were measured within varying concentration of MEG solution (0, 30, 40, 50, 60, 70, and 80 wt %) and at varying temperature (25, 30, 40, 50, 60, 70, and 80 degrees C). Thermodynamic properties of the dissociation process including Gibbs free energy (Delta G degrees kJ mol(-1)), standard enthalpy (Delta H degrees kJ mol(-1)), and entropy (Delta S degrees kJ mol(-1) K-1) were calculated at 25 degrees C using the van't Hoff equation. Comparison of the reported experimental pK(a) values and calculated thermodynamic properties in aqueous solution to the literature demonstrated good agreement. Two models have been proposed to calculate the pK(a) of acetic acid and MDEA within MEG solutions of varying concentration, temperature, and ionic strength. The proposed models have an average error of 0.413% and 0.265% for acetic acid and MDEA, respectively.